Method for encoding and decoding image and device using same

ABSTRACT

The method for deriving a temporal motion vector predictor according to the present invention comprises the steps of: selecting a reference picture for a current block; deciding a predictor block corresponding to a predetermined storage unit block, as a reference prediction unit for the current block, in the reference picture; and deriving the temporal motion vector predictor from motion information of the decided reference prediction unit. The present invention enhances image compression efficiency.

This application is a Continuation of U.S. patent application Ser. No.14/660,425 filed on Mar. 17, 2015, which is a Continuation of U.S.patent application Ser. No. 13/814,751 filed on Feb. 7, 2013, which isthe National Phase Application No. PCT/KR2012/000959 filed on Feb. 9,2012, which claims the benefit of U.S. Provisional Application No.61/440,871, filed on Feb. 9, 2011; 61/454,567, filed on Mar. 20, 2011and 61/476,776, filed on Apr. 19, 2011, the entire contents of which arehereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates generally to image processing, and moreparticularly to a method and apparatus for inter prediction.

BACKGROUND ART

Recently, the demand for high-resolution and high-quality images, suchas High Definition (HD) images and Ultra High Definition (UHD) imageshas been increasing in various fields. As the resolution and picturequality of image data becomes higher, the amount of information oramount of bits that are transmitted is correspondingly increased,relative to existing image data. Accordingly, in the case oftransmitting image data using a medium such as an existing wire/wirelessline, or in the case of storing image data using an existing storagemedium, transmission costs and storage costs are increased. In order tosolve these problems, high-efficiency image compression techniques maybe used.

There are various image compression techniques, such as an interprediction technique that predicts pixel values included in the currentpicture from a picture that is before or after the current picture, anintra prediction technique that predicts pixel values included in thecurrent picture using pixel information from the current picture, and anentropy encoding technique that allocates a short codeword to a valuehaving a high appearance frequency and allocates a long codeword to avalue having a low appearance frequency. Image data can be effectivelycompressed to be transmitted or stored using such image compressiontechniques.

DISCLOSURE Technical Problem

An aspect of the present invention provides a method and apparatus forencoding an image, which can improve image compression efficiency.

Another aspect of the present invention provides a method and apparatusfor decoding an image, which can improve image compression efficiency.

Still another aspect of the present invention provides a method andapparatus for inter prediction, which can improve image compressionefficiency.

Still yet another aspect of the present invention provides a method andapparatus for deriving a temporal motion vector predictor, which canimprove image compression efficiency.

Technical Solution

1. An exemplary embodiment of the present invention provides a methodfor deriving a temporal motion vector predictor. The method includesselecting a reference picture for a current block; determining aprediction block that corresponds to a predetermined storage unit blockin the reference picture as a reference prediction unit (colPu) for thecurrent block; and deriving a temporal motion vector predictor (TMVP)from the motion information of the determined reference prediction unit.Here, the motion information of the reference prediction unit is motioninformation located in a representative pixel that the referenceprediction unit covers, and the representative pixel is a pixel in whichrepresentative motion information, which is stored to represent themotion information in the predetermined storage unit block, is located.

2. According to 1, the predetermined storage unit block is a bottomright corner block that is located at a bottom right corner of aco-located block, and the co-located block is a block that is in thesame position as the current block in the reference picture.

3. According to 2, if the prediction block that corresponds to thebottom right corner block in the reference picture is coded in an intramode or is unavailable, the predetermined storage unit block is a bottomright center block that is located in a bottom right center of theco-located block.

4. According to 2, if the bottom right corner block is located outsidethe Largest Coding Unit (LCU) to which the current block belongs, thepredetermined storage unit block is a bottom right center block that islocated in a bottom right center of the co-located block.

5. According to 2, if the prediction block that corresponds to thebottom right corner block in the reference picture is coded in an intramode or is unavailable, the predetermined storage unit block is a topleft center block that is located in a top left center of the co-locatedblock.

6. According to 1, the predetermined storage unit block is a top leftcenter block located at a top left center of a co-located block, and theco-located block is a block that is in the same position as the currentblock in the reference picture.

7. According to 1, the predetermined storage unit block is a bottomright center block located at a bottom right center of a co-locatedblock, and the co-located block is a block that is in the same positionas the current block in the reference picture.

8. Another exemplary embodiment of the present invention provides amethod for deriving a temporal motion vector predictor. The methodincludes selecting a reference picture for a current block; scanning aplurality of predetermined storage unit blocks in the reference picturein a predetermined order; selecting the storage unit block whichincludes available motion information and has the highest scanningpriority among the plurality of the predetermined storage unit blocks;determining a prediction unit that corresponds to the selected storageunit block in the reference picture as a reference prediction unit(colPu); and deriving a temporal motion vector predictor (TMVP) frommotion information of the determined reference prediction unit. Here,the motion information of the reference prediction unit is motioninformation located in a representative pixel that the referenceprediction unit covers, and the representative pixel is a pixel in whichrepresentative motion information, which is stored to represent themotion information in the selected storage unit block, is located.

9. Still another exemplary embodiment of the present invention providesa method for inter prediction. The method includes selecting a referencepicture for a current block; determining a prediction block thatcorresponds to a predetermined storage unit block in the referencepicture as a reference prediction unit (colPu) for the current block;deriving a temporal motion vector predictor (TMVP) from motioninformation of the determined reference prediction unit; and generatinga prediction block for the current block using the derived temporalmotion vector predictor. Here, the motion information of the referenceprediction unit is motion information located in a representative pixelthat the reference prediction unit covers, and the representative pixelis a pixel in which representative motion information, which is storedto represent the motion information in the predetermined storage unitblock, is located.

10. According to 9, the predetermined storage unit block is a bottomright corner block that is located at a bottom right corner of aco-located block, and the co-located block is a block that is in thesame position as the current block in the reference picture.

11. According to 10, if the prediction block that corresponds to thebottom right corner block in the reference picture is coded in an intramode or is unavailable, the predetermined storage unit block is a bottomright center block that is located in a bottom right center of theco-located block.

12. According to 10, if the bottom right corner block is located outsidethe Largest Coding Unit (LCU) to which the current block belongs, thepredetermined storage unit block is a bottom right center block that islocated in a bottom right center of the co-located block.

Advantageous Effects

According to the method for encoding an image according to theembodiment of the present invention, image compression efficiency can beimproved.

According to the method for decoding an image according to theembodiment of the present invention, image compression efficiency can beimproved.

According to the method for inter prediction according to the embodimentof the present invention, image compression efficiency can be improved.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram schematically illustrating an apparatus forencoding an image according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram schematically illustrating a predictoraccording to an embodiment of the present invention.

FIG. 3 is a block diagram schematically illustrating an apparatus fordecoding an image according to an embodiment of the present invention.

FIG. 4 is a conceptual diagram schematically illustrating a predictor ofan apparatus for decoding an image according to an embodiment of thepresent invention.

FIG. 5 is a flowchart schematically illustrating an embodiment of amethod for deriving a motion vector in the case where an advanced motionvector predictor (AMVP) is applied in an inter prediction mode.

FIG. 6 is a conceptual diagram schematically illustrating an embodimentof a method for generating a motion vector predictor candidate list.

FIG. 7 is a conceptual diagram schematically illustrating an embodimentof a storage unit block.

FIG. 8 is a conceptual diagram schematically illustrating anotherembodiment of a storage unit block.

FIG. 9 is a conceptual diagram schematically illustrating an embodimentof a method for compressing temporal motion information.

FIG. 10 is a conceptual diagram schematically illustrating anotherembodiment of a method for compressing temporal motion information.

FIG. 11 is a conceptual diagram schematically illustrating still anotherembodiment of a method for compressing temporal motion information.

FIG. 12 is a conceptual diagram schematically illustrating still anotherembodiment of a method for compressing temporal motion information.

FIG. 13 is a conceptual diagram schematically illustrating still anotherembodiment of a method for compressing temporal motion information.

FIG. 14 is a conceptual diagram schematically illustrating still anotherembodiment of a method for compressing temporal motion information.

FIG. 15 is a conceptual diagram schematically illustrating still anotherembodiment of a method for compressing temporal motion information.

FIG. 16 is a conceptual diagram schematically illustrating a co-locatedblock included in a reference picture.

FIG. 17 is a conceptual diagram schematically illustrating an embodimentof a method for deriving a temporal motion vector predictor.

FIG. 18 is a conceptual diagram schematically illustrating an embodimentof a temporal reference block in which a temporal motion vectorpredictor may be located.

FIG. 19 is a conceptual diagram schematically illustrating anotherembodiment of a method for deriving a temporal motion vector predictor.

FIG. 20 is a conceptual diagram schematically illustrating still anotherembodiment of a method for deriving a temporal motion vector predictor.

FIG. 21 is a conceptual diagram schematically illustrating still anotherembodiment of a method for deriving a temporal motion vector predictor.

FIG. 22 is a conceptual diagram schematically illustrating still anotherembodiment of a method for deriving a temporal motion vector predictor.

FIG. 23 is a flowchart schematically illustrating a method for interprediction according to an embodiment of the present invention.

MODE FOR INVENTION

Since the present invention may have various modifications and severalembodiments, specified embodiments will be exemplified in the drawingsand will be described in detail. However, the present invention is notlimited to such specified embodiments. The terms used in the descriptionare used to explain the specified embodiments only, but are not intendedto limit the technical idea of the present invention. In thedescription, a singular expression may include a plural expressionunless specially described. The terms “includes” or “has” used in thedescription mean that one or more other components, steps, operationsand/or existence or addition of elements are not excluded in addition tothe described components, steps, operations and/or elements.

On the other hand, respective configurations in the drawings, which willbe described in the present invention, are independently illustrated forconvenience of explanation of different functions in an videoencoding/decoding apparatus, but do not mean that the configurations areimplemented by separate hardware or separate software. For example, twoor more configurations may be combined into one configuration, or oneconfiguration may be divided into plural configurations. Even theembodiments in which the respective configurations are integrated and/orseparated are included in the scope of the present invention unless theydepart from the essential features of the present invention.

Further, some of constituent elements may not be essential constituentelements for performing the essential functions of the presentinvention, but may only be selective constituent elements for improvingperformance. The present invention may be implemented to include onlythe essential configuration that is necessary to implement the essentialfeatures of the present invention, excluding the constituent elementsused to improve only performance, and additionally the structure thatincludes only the essential constituent elements excluding the selectiveconstituent elements used to improve only performance is included in thescope of the present invention.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. In theentire description of the present invention, the same drawing referencenumerals are used for the same elements across various figures, andduplicate explanation of the same elements will be omitted.

FIG. 1 is a block diagram schematically illustrating an apparatus forencoding an image according to an embodiment of the present invention.Referring to FIG. 1, an apparatus 100 for encoding an image includes apicture divider 105, a predictor 110, a transformer 115, a quantizer120, a reordering module 125, an entropy encoder 130, an dequantizer135, an inverse transformer 140, a filter module 145, and a memory 150.

The picture divider 105 may divide an input picture into at least oneprocessing unit. At this time, the processing unit may be a predictionunit (PU), a transform unit (TU), or a coding unit (CU).

The predictor 110, to be described later, may include an inter predictorthat performs inter prediction and an intra predictor that performsintra prediction. The predictor 110 may perform prediction with respectto the picture processing unit in the picture divider 105 and generateprediction blocks. The picture processing unit in the predictor 110 maybe a coding unit, a transform unit, or a prediction unit. Further, thepredictor 110 may determine whether the prediction that is performedwith respect to the corresponding processing unit is inter prediction orintra prediction, and determine the detailed contents (for example,prediction mode and the like) of the prediction method. At this time,the processing unit for performing the prediction may be different fromthe processing unit in which the prediction method and the detailedcontents are determined. For example, the prediction method and theprediction mode may be determined in the prediction unit, and theprediction performance may be performed in the transform unit. Theresidual value (residual block) between the generated prediction blockand the original block may be input to the transformer 115. Further,prediction mode information, motion vector information and the like thatare used for the prediction may be encoded by the entropy encoder 130together with the residual value, and then transferred to a decoder.

The transformer 115 performs the transform of the residual blocks in thetransform unit and generates transform coefficients. The transform maybe performed by the transformer 115 in the transform unit which may havea quad tree structure. At this time, the size of the transform unit maybe determined within a range of predetermined maximum and minimum sizes.The transformer 115 may transform the residual blocks using a DiscreteCosine Transform (DCT) and/or a Discrete Sine Transform (DST).

The quantizer 120 may generate quantization coefficients by quantizingthe residual values transformed by the transformer 115. The valuescalculated by the quantizer 120 may be provided to the dequantizer 135and the reordering module 125.

The reordering module 125 reorders the quantization coefficientsprovided from the quantizer 120. By reordering the quantizationcoefficients, the encoding efficiency in the entropy encoder 130 can beimproved. The reordering module 125 may reorder the 2D block typequantization coefficients in 1D vector form through a coefficientscanning method. The reordering module 125 may heighten the entropyencoding efficiency of the entropy encoder 130 by changing the order ofcoefficient scanning based on the probable statistics of thecoefficients transmitted from the quantizer.

The entropy encoder 130 may perform entropy encoding on the quantizationcoefficients reordered by the reordering module 125. The entropy encoder130 may encode various information, such as quantization coefficientinformation of the encoding unit transferred from the reordering module125 and the predictor 110, block type information, prediction modeinformation, division unit information, prediction unit information andtransmission unit information, motion vector information, referencepicture information, interpolation information of blocks, and filteringinformation.

For entropy encoding, encoding methods, such as exponential Golomb,Context-Adaptive Variable Length Coding (CAVLC), and Context-AdaptiveBinary Arithmetic Coding (CABAC), may be used. For example, a table forperforming entropy encoding, such as Variable Length Coding (hereinafterreferred to as “VLC”), may be stored in the entropy encoder 130, and theentropy encoder 130 may perform the entropy encoding using the VLC tablestored therein. As another embodiment, in the CABAC entropy encodingmethod, the entropy encoder 130 converts symbols into bins by binarizingthe symbols, and performs arithmetic encoding on the bins depending onthe bin occurrence probability to generate a bit stream.

In the case where the entropy encoding is applied, an index of a lowvalue and the corresponding short codeword may be allocated to a symbolhaving a high occurrence probability, and an index of a high value andthe corresponding long codeword may be allocated to a symbol having alow occurrence probability. Accordingly, the amount of bits for theencoding target symbols may be reduced, and image compressionperformance may be improved by the entropy encoding.

The dequantizer 135 may perform dequantization on the values quantizedby the quantizer 120, and the inverse transformer 140 may performinverse transformation on the values dequantized by the dequantizer 135.The residual values generated by the dequantizer 135 and the inversetransformer 140 may be added to the prediction block predicted by thepredictor 110 to generate a reconstructed block.

The filter module 145 may apply a deblocking filter and/or an AdaptiveLoop Filter (ALF) to the reconstructed picture.

The deblocking filter can remove block distortion that occurs on aboundary between blocks in the reconstructed picture. The ALF mayperform filtering based on a value obtained by comparing thereconstructed image with the original image after the block is filteredthrough the deblocking filter. The ALF may operate only in the casewhere high efficiency of the image is applied.

On the other hand, the filter module 145 may not perform filtering onthe reconstructed blocks used for inter prediction.

The memory 150 may store the reconstructed block or picture calculatedthrough the filter module 145. The reconstructed block or picture storedin the memory 150 may be provided to the predictor 110 that performsinter prediction.

The coding unit (CU) is a unit in which picture encoding/decoding isperformed, and may be divided to have a depth based on the quad treestructure. The coding unit may have various sizes, such as 64×64, 32×32,16×16, and 8×8.

The encoder may transmit information on the largest coding unit (LCU)and the smallest coding unit (SCU) to the decoder. Information (depthinformation) on the number of divisions may be transmitted to thedecoder together with the information on the largest coding unit and/orthe smallest coding unit. The information on whether the coding unit isdivided based on the quad tree structure may be transferred from theencoder to the decoder through flag information such as a split flag.

One coding unit may be divided into a plurality of prediction units. Inthe case where the intra prediction is performed, the prediction modemay be determined in the prediction unit, and the prediction may beperformed in the prediction unit. At this time, the prediction mode maybe determined in the prediction unit, and the intra prediction may beperformed in the transform unit.

FIG. 2 is a conceptual diagram schematically illustrating a predictoraccording to an embodiment of the present invention. Referring to FIG.2, a predictor 200 may include an inter predictor 210 and an intrapredictor 220.

The inter predictor 210 may generate a prediction block by performingprediction based on information of at least one picture of a previouspicture and a subsequent picture of the current picture. Further, theintra predictor 220 may generate a prediction block by performingprediction based on pixel information in the current picture.

The inter predictor 210 may select a reference picture for theprediction unit and select a reference block having the same size as theprediction unit in an integer number pixel sample unit. Then, the interpredictor 210 may generate a prediction block which is most similar tothe current prediction unit to minimize the residual signal and also tominimize the size of a motion vector being encoded, in the unit below aninteger, such as ½ pixel sample unit and ¼ pixel sample unit. At thistime, the motion vector may be expressed in the unit below an integerpixel, for example, in ¼ pixel unit for a luma pixel and in ⅛ pixel unitfor a chroma pixel.

Information on the index of the reference picture and the motion vectorselected by the inter predictor 210 may be encoded and transferred tothe decoder.

FIG. 3 is a block diagram schematically illustrating an apparatus fordecoding an image according to an embodiment of the present invention.Referring to FIG. 3, an video decoder 300 may include an entropy decoder310, a reordering module 315, an dequantizer 320, an inverse transformer325, a predictor 330, a filter module 335, and a memory 340.

If an image bit stream is input to the video decoder, the input bitstream may be decoded through an image information processing procedurein the video encoder.

The entropy decoder 310 may perform entropy decoding on the input bitstream, and an entropy decoding method is similar to the above-describedentropy encoding method. For example, if the Variable Length Coding(hereinafter referred to as “VLC”) such as CAVLC is used to perform theentropy encoding in the video encoder, the entropy decoder 310 mayperform the entropy decoding by implementing the same VLC table as theVLC table used in the encoder. Even in the case where CABAC is used toperform the entropy encoding in the video encoder, the entropy decoder310 may perform the corresponding entropy decoding using CABAC.

In the case where the entropy decoding is applied, an index of a lowvalue and the corresponding short codeword may be allocated to a symbolhaving a high occurrence probability, and an index of a high value andthe corresponding long codeword may be allocated to a symbol having alow occurrence probability. Accordingly, the bit rate for the encodingtarget symbols may be reduced, and the image compression performance maybe improved by the entropy encoding.

Information to generate a prediction block of the information decoded bythe entropy decoder 310 may be provided to the predictor 330, and theresidual value, of which the entropy decoding has been performed by theentropy decoder, may be input to the reordering module 315.

The reordering module 315 may reorder the bit stream entropy-decoded bythe entropy decoder 310 based on the reordering method in the videoencoder. The reordering module 315 may reconstruct coefficients in aone-dimensional vector form into those in a two-dimensional block formin order for reordering. The reordering module 315 may receiveinformation related to the coefficient scanning performed by the encoderand perform the reordering through an inverse scanning method based onthe order of scanning performed by the corresponding encoder.

The dequantizer 320 may perform dequantization based on quantizationparameters provided from the encoder and the coefficient values of thereordered blocks.

The inverse transformer 325 may perform inverse DCT and/or inverse DCTagainst the DCT and DST performed by the transformer of the encoder withrespect to the results of quantization performed in the video encoder.The inverse transformation may be performed based on the transmissionunit or image division unit determined by the encoder. The transformerof the encoder may selectively perform the DCT and/or DST depending onplural sheets of information, such as the prediction method, the size ofthe current block, and the prediction direction, and the inversetransformer 325 of the decoder may perform the inverse transform basedon the transform information performed by the transformer of theencoder.

The predictor 330 may generate a prediction block based on theinformation related to the prediction block generation provided from theentropy decoder 310 and the previously decoded block and/or pictureinformation provided from the memory 340. A reconstructed block may begenerated using the prediction block generated from the predictor 330and the residual block provided from the inverse transformer 325.

The reconstructed block and/or picture may be provided to the filtermodule 335. The filter module 335 may apply deblocking filtering, SampleAdaptive Offset (SAO) and/or adaptive loop filtering (ALF) to thereconstructed block and/or picture.

The memory 340 may store and use the reconstructed picture or block asthe reference picture or reference block, and may provide thereconstructed picture to an output section.

FIG. 4 is a conceptual diagram schematically illustrating a predictor ofan apparatus for decoding an image according to an embodiment of thepresent invention.

Referring to FIG. 4, a predictor 400 may include an intra predictor 410and an inter predictor 420.

The intra predictor 410 may generate a prediction block based on thepixel information in the current picture if the prediction mode for thecorresponding prediction unit is an intra prediction mode (intra-frameprediction mode).

If the prediction mode of the corresponding prediction unit is an interprediction mode (inter-frame prediction mode), the inter predictor 420may perform the inter prediction on the current prediction unit based onthe information included in at least one picture of the previous pictureand the subsequent picture of the current picture, including the currentprediction unit using the information that is necessary for the interprediction of the current prediction unit provided from the videoencoder, for example, information on the motion vector and the referencepicture index.

At this time, if a skip flag, a merge flag, and the like, of theencoding unit received from the encoder is confirmed, the motioninformation may be derived depending on such flags.

Hereinafter, in the case where the “image” or “frame” can represent thesame meaning as the “picture” according to the configuration orexpression of the invention, the “picture” may be described as the“image” or “frame”. Further, the inter prediction and the inter-frameprediction have the same meaning, and the intra prediction and theintra-frame prediction have the same meaning.

In the case of the inter prediction mode, the encoder and the decodermay derive motion information from the current block and perform interprediction on the current block based on the derived motion information.

FIG. 5 is a flowchart schematically illustrating an embodiment of amethod for deriving a motion vector in the case where an advanced motionvector predictor (AMVP) is applied in an inter prediction mode.

Referring to FIG. 5, the encoder and the decoder may generate a motionvector predictor candidate list for the current block (S510). Here, themotion vector predictor (MVP) may indicate a prediction value for themotion vector of the current block. Hereinafter, the motion vectorpredictor and the MVP have the same meaning.

The encoder and the decoder may generate the motion vector predictorcandidate list using motion vectors of available neighboring blocks thatare adjacent to the current block and/or temporal reference blocksincluded in the respective reference pictures. The temporal referenceblock may be derived based on blocks of the respective referencepictures co-located with the current block (hereinafter, for conveniencein explanation, referred to as “co-located blocks”). The detailedembodiment of a method for deriving the temporal reference blocks willbe described later.

The encoder and the decoder may select a motion vector predictor for thecurrent block from among the motion vector predictor candidates includedin the motion vector predictor candidate list (S520).

The encoder may select an optimum motion vector predictor for thecurrent block by applying a motion vector competition (hereinafterreferred to as a “MVC”) to the motion vector predictor candidatesincluded in the motion vector predictor candidate list. If the motionvector predictor is selected, the encoder may transmit a motion vectorpredictor index to the decoder through the bit stream. Here, the motionvector predictor index means an index that indicates the motion vectorpredictor of the current block, that is selected from the motion vectorpredictor candidates included in the motion vector predictor candidatelist.

The decoder may receive the motion vector predictor index from theencoder. The decoder may select the motion vector predictor for thecurrent block from among the motion vector predictor candidates includedin the motion vector predictor candidate list using the received motionvector predictor index.

The decoder may derive the motion vector of the current block using theselected motion vector predictor (S530).

If the motion vector predictor for the current block is selected, theencoder may obtain a difference between the motion vector of the currentblock and the motion vector predictor. Hereinafter, the differencebetween the motion vector and the motion vector predictor is called amotion vector difference (MVD). The encoder may transmit information onthe motion vector difference, rather than the motion vector itself, tothe decoder. At this time, as the motion vector difference becomessmaller, the amount of information that is transmitted from the encoderto the decoder can be reduced.

The decoder may receive the information on the motion vector differencefrom the encoder. If the motion vector predictor for the current blockis selected, the decoder may obtain the motion vector of the currentblock by adding the selected motion vector predictor and the motionvector difference with each other.

FIG. 6 is a conceptual diagram schematically illustrating an embodimentof a method for generating a motion vector predictor candidate list.

Hereinafter, one group that includes a bottom left corner block (A₀) 610of the current block and a block (A₁) 620 located at the lowest endamong blocks adjacent to the left side of the current block is called aleft candidate block group. Further, one group that includes a top rightcorner block (B₀) 630 of the current block, a block (B₁) 640 located onthe top side among the blocks adjacent to a top end of the currentblock, and a top left corner block (B₂) 650 of the current block iscalled a top candidate block group.

The encoder and the decoder may derive one motion vector predictorcandidate from the left candidate block group. Here, the motion vectorpredictor candidate derived from the left candidate block group may berepresented by MV_(A). For example, the encoder and the decoder mayselect the motion vector of the first block which is available and hasthe same reference picture index as the current block as the motionvector predictor candidate MV_(A) of the current block while scanningthe blocks included in the left candidate block group in the order ofA₀→A₁.

The encoder and the decoder may derive one motion vector predictorcandidate from the top candidate block group. Here, the motion vectorpredictor candidate derived from the top candidate block group may berepresented by MV_(B). For example, the encoder and the decoder mayselect the motion vector of the first block which is available and hasthe same reference picture index as the current block as the motionvector predictor candidate MV_(B) of the current block while scanningthe blocks included in the top candidate block group in the order ofB₀→B₁→B₂.

Further, the encoder and the decoder may select the motion vector of thetemporal reference block (Col) 660 in the reference picture as themotion vector predictor candidate of the current block. Here, the motionvector of the temporal reference block 660 may be represented byMV_(col).

In the above-described embodiment, the motion vector predictor candidatederived from the left candidate block group and the motion vectorpredictor candidate derived from the top candidate block group may becalled spatial motion vector predictors. Further, the motion vectorpredictor candidate derived from the temporal reference block in thereference picture may be called a temporal motion vector predictor(TMVP). Accordingly, the motion vector predictor candidates may includethe spatial motion vector predictor and the temporal motion vectorpredictor, and the motion vector predictor candidate list may includethe spatial motion vector predictor and/or the temporal motion vectorpredictor.

The encoder and the decoder may remove duplicate candidates from amongthe motion vector predictor candidates selected by the above-describedmethod. The encoder and the decoder may construct the motion vectorpredictor candidate list using the remaining motion vector predictorcandidates.

When motion vector prediction is performed, not only the spatial motionvector predictor but also the temporal motion vector predictor (TMVP)may be used as the motion vector predictor candidates. As describedabove, the temporal motion vector predictor may mean the motion vectorpredictor candidate derived from the temporal reference block in thereference picture (for example, picture which is adjacent to the currentpicture or is close in temporal distance to the current picture).Hereinafter, the motion vector in the reference picture, which includesthe temporal motion vector predictor, is called the temporal motionvector. Further, the motion information (for example, the motion vectorand the reference picture index) in the reference picture is calledtemporal motion information.

In order to derive the temporal motion vector predictor for the currentblock, it is necessary that the motion information of the previouslydecoded picture is stored. Accordingly, when the decoded picture and/orblock is stored in the memory (a reference picture buffer and/or adecoded picture buffer (DPB), the decoded motion information may bestored together with the decoded picture and/or block. The memory inwhich the motion information is stored may also be called a motionvector memory and/or motion vector buffer.

As an embodiment, the motion information may be stored for each minimumunit block. Here, the minimum unit block means a block in the minimumstorage unit in which the motion information is stored. Hereinafter, theblock in the minimum storage unit in which the motion information isstored is called the minimum unit block, and as an embodiment, the sizeof the minimum unit block may be 4×4.

However, if the size of the picture is large, the size of the memorythat is necessary to store the motion information may become larger. Inconsideration of granularity of the motion information and the pointthat two motion vectors may be used for one block in a B slice, the sizeof the memory for storing the motion information is important.Accordingly, a temporal motion information compression technique may beused to reduce the size of the required memory and the memory accessbandwidth.

As an embodiment of the temporal motion information compressiontechnique, a median filter may be used to store the motion informationwith the granularity that is larger than the decoded motion information.In the case where the median filter is applied to the motion vector,filtering and/or compression may be performed with respect to eachcomponent of the motion vector. The motion information compressionprocess using the median filter may be performed before the decodedpicture which has passed through the adaptive loop filter is stored inthe memory.

The median filter may be applied based on the storage unit that isderived by a predetermined storage unit and/or a predetermined method.Here, the storage unit may mean the unit in which the motion informationis compressed and stored. Hereinafter, the block that indicates the unitin which the motion information is compressed and stored is called astorage unit block.

The predetermined storage unit may be a block having a predeterminedsize that is larger than the size (for example, 4×4) of the minimum unitblock. Further, the storage unit may be derived using the compressioninformation from the encoder. Here, the compression information mayinclude a compression flag and compression ratio information. Thecompression flag may be a flag that indicates whether the motioninformation compression is applied, and the compression ratioinformation may indicate the compression ratio of the motioninformation. Since a method for transmitting the compression informationand a method for deriving the storage unit using the compressioninformation are identical to the motion information compressiontechnique not using the median filter, as described later, thedescription thereof will be omitted.

In the above-described motion information compression process, themotion information can be stored with low resolution, and thus the sizeof the memory necessary for storing the motion information can bereduced.

As another embodiment of the temporal motion information compressiontechnique, the method for storing the motion information that does notuse the median filter may be provided.

In this method, a representative motion vector may be selected among themotion vectors in the storage unit block, and the selectedrepresentative motion vector may be allocated to all minimum unit blocksin the storage unit block. Accordingly, the motion information can bestored with low resolution, and thus the size of the memory for storingthe motion information can be reduced. In the case where therepresentative motion vector is used rather than the median filter, thecoding efficiency may be somewhat lowered in comparison to the casewhere the median filter is used, but the computation amount and/orcomplexity may be reduced. Hereinafter, embodiments of the method notusing a median filter for storing the motion information will bedescribed.

FIG. 7 is a conceptual diagram schematically illustrating an embodimentof a storage unit block.

It is assumed that coordinates of a certain pixel in the storage unitblock are in the format of (x, y), and the width and the height of thestorage unit block are defined as variables W and H, respectively. Thenumber and the size of the minimum unit blocks included in the storageunit block are not limited to the embodiment in FIG. 7, and for example,the number of the minimum unit blocks included in the storage unit blockmay be larger or smaller than 16.

Hereinafter, in embodiments in FIGS. 8 to 15, the wording is defined andused in a manner wherein the minimum unit block including pixels whichexist in ((x>>log₂ W)<<log₂ W, (y>>log₂ H)<<log₂ H) is a top left block710, the minimum unit block including pixels which exist in (((x>>log₂W)<<log₂ W)+W−1, (y>>log₂ H)<<log₂ H) is a top right block 720, theminimum unit block including pixels which exist in ((x>>log₂ W)<<log₂ W,((y>>log₂ H)<<log₂ H)+H−1) is a bottom left block 730, and the minimumunit block including pixels which exist in (((x>>log₂ W)<<log₂ W)+W−1,((y>>log₂ H)<<log₂ H)+H−1) is a bottom right block 740.

Further, the wording is defined and used in a manner wherein the minimumunit block including pixels which exist in (((x>>log₂ W)<<log₂ W)+W/2−1,((y>>log₂ H)<<log₂ H)+H/2−1) is a top left center block 750, the minimumunit block including pixels which exist in (((x>>log₂ W)<<log₂ W)+W/2,((y>>log₂ H)<<log₂ H)+H/2−1) is a top right center block 760, theminimum unit block including pixels which exist in (((x>>log₂ W)<<log₂W)+W/2−1, ((y>>log₂ H)<<log₂ H)+H/2) is a bottom left center block 770,and the minimum unit block including pixels which exist in (((x>>log₂W)<<log₂ W)+W/2, ((y>>log₂ H)<<log₂ H)+H/2) is a bottom right centerblock 780.

Here, the respective blocks (the top left block 710, the top right block720, the bottom left block 730, the bottom right block 740, the top leftcenter block 750, the top right center block 760, the bottom left centerblock 770, and the bottom right center block 780) may be specified bythe coordinates of the pixels included therein as described above. Forexample, if the size of the storage unit block is 16×16, the top leftblock may be specified by ((x>>4)<<4, (y>>4)<<4).

FIG. 8 is a conceptual diagram schematically illustrating anotherembodiment of a storage unit block.

The storage unit block may represent a unit in which the motioninformation is compressed and stored. The storage unit block may be ablock having a predetermined size that is larger than the minimum unitblock (for example, a block having 4×4 size), and for example, a blockhaving a 16×16 size may be used as the storage unit block. At this time,as an embodiment, each of 16 minimum unit blocks included in the storageunit block may have one piece of motion information.

Further, the storage unit may be derived using the compressioninformation transmitted from the encoder. Here, the compressioninformation may be the compression flag and the compression ratioinformation. The compression flag may indicate whether the motioninformation compression process is applied, and the compression ratioinformation may indicate the compression ratio of the motioninformation.

The compression information may be included in a Sequence Parameter Set(SOS), a Picture Parameter Set (PPS), or a slice header and may betransmitted from the encoder to the decoder. Table 1 below shows anembodiment of an SPS in which the compression information is defined. Inthe embodiment of Table 1, although the compression information isdefined in the SPS, it may be defined in the PPS or the slice header.

TABLE 1 C Descriptor seq_parameter_set_rbsp( ) { .....motion_vector_buffer_comp_flag 0 u(1) if( motion_vector_buffer_comp_flag) motion_vector_buffer_comp_ratio_log2 0 u(8) rbsp_trailing_bits( ) 0 }

Here, motion_vector_buffer_com_flag may correspond to the compressionflag status. For example, if motion_vector_buffer_com_flag is 1, thecompression flag may indicate that the motion vector memory compressionprocess is performed.

Here, motion_vector_buffer_com_ratio_log 2 may correspond to thecompression ratio information, and if motion_vector_buffer_com_ratio_log2 does not exist in the SPS, the value ofmotion_vector_buffer_com_ratio_log 2 may be inferred to 0. At this time,as an example, the motion vector memory compression ratio may berepresented by Equation 1 below.MVBufferCompRatio=1<<motion_vector_buffer_comp_ratio_log 2ormotion_vector_buffer_comp_ratio=1<<motion_vector_buffer_comp_ratio_log2  [Equation 1]

Here, MVBufferCompRatio and motion_vector_buffer_comp_ratio mayrepresent the motion vector memory compression ratio. For example, ifthe value of motion_vector_buffer_comp_ratio_log 2 is 2, the value ofMVBufferCompRatio and motion_vector_buffer_comp_ratio may be 4.

Referring to FIG. 8, as an embodiment, if motion_vertor_buffer_comp_flagis 1, and motion_vector_buffer_comp_ratio is 4, the storage unit blockmay be configured as 16 minimum unit blocks in total, which are arrangedby 4 lines in width and 4 lines in length, that is, which are in a 4×4(MVBufferCompRatio-by-MVBufferCompRatio ormotion_vector_buffer_comp_ratio-by-motion_vector_buffer_comp_ratio)form. Here, the storage unit block may always have a square shape. Atthis time, each of the 16 minimum unit blocks that constitute thestorage unit block may be a block having a 4×4 size, and may have onemotion vector. At this time, the overall size of the storage unit blockis 16×16, and one storage unit block may have 16 motion vectors.

Table 2 below shows another embodiment of the SPS (or PPS or sliceheader) in which the compression information is defined.

TABLE 2 C Descriptor seq_parameter_set_rbsp( ) { or PPS or Slice header..... motion_data_buffer_comp_flag 0 u(1) if(motion_data_buffer_comp_flag ) motion_data_buffer_comp_ratio_log2 0 u(8)rbsp_trailing_bits( ) 0 }

Here, motion_data_buffer_comp_flag may correspond to the compressionflag that indicates whether the motion information memory compressionprocess is applied. For example, if motion_data_buffer_comp_flag is 1,the compression flag may indicate that the motion information memorycompression process is performed.

Here, motion_data_buffer_comp_ratio_log 2 may correspond to thecompression ratio information that indicates the compression ratio ofthe motion information. At this time, the motion vector memorycompression ratio may be derived by the same method as that in Equation1, and the storage unit block may always have a square shape. Forexample, if motion_data_buffer_comp_ratio_log 2 is 1, the size of thestorage unit block may become 8×8, if motion_data_buffer_comp_ratio_log2 is 2, the size of the storage unit block may become 16×16, and ifmotion_data_buffer_comp_ratio_log 2 is 3, the size of the storage unitblock may become 32×32. As another embodiment,motion_data_buffer_comp_ratio_log 2 may be defined in the unit of aninteger rather than through a log scale. For example, ifmotion_data_buffer_comp_ratio_log 2 is 1, the size of the storage unitblock may become 8×8, if motion_data_buffer_comp_ratio_log 2 is 2, thesize of the storage unit block may become 12×12, and ifmotion_data_buffer_comp_ratio_log 2 is 3, the size of the storage unitblock may become 16×16.

Table 3 below shows still another embodiment of the SPS (or PPS or sliceheader) in which the compression information is defined.

TABLE 3 C Descriptor seq_parameter_set_rbsp( ) { or PPS or Slice header..... motion_date_buffer_comp_flag 0 u(1) if(motion_data_buffer_comp_flag ) { motion_data_buffer_comp_ratio_x_log2 0u(8) motion_data_buffer_comp_ratio_y_log2 0 u(8) } rbsp_trailing_bits( )0 }

Here, motion_data_buffer_comp_ratio_x_log 2 andmotion_data_buffer_comp_ratio_y_log 2 may correspond to the compressionratio information that indicates the compression ratio of the motioninformation. Further, motion_data_buffer_comp_ratio_x_log 2 may indicatethe compression ratio in the x-axis direction (horizontal direction) ofthe motion information, and motion_data_buffer_comp_ratio_y_log 2 mayindicate the compression ratio in the y-axis direction (verticaldirection) of the motion information. In the embodiment of Table 3,since the compression ratio in the x-axis direction and the compressionratio in the y-axis direction are separately defined, the storage unitblock may have a rectangular shape rather than a square shape.

In the above-described embodiments, the compression information isdefined in the SPS, PPS, or slice header. However, depending on theimplementation and/or need, the compression information may be definedin a profile and/or level.

As described above, the storage unit block and/or the minimum unit blockmay be determined by way of various methods. In embodiments of themethod for compressing the temporal motion information to be describedlater, for convenience in explanation, it is assumed that the size ofthe storage unit block is 16×16, and the size of the minimum unit blockis 4×4. Further, it is assumed that one storage unit block includes 16minimum unit blocks which are arranged in a 4×4 form.

FIG. 9 is a conceptual diagram schematically illustrating an embodimentof a method for compressing temporal motion information. In FIG. 9, (X0,Y0) to (X15, Y15) represent motion vectors, and ref_idx n (n is aninteger that is equal to or larger than 0) represent reference pictureindexes. The temporal motion information compression process may beperformed before the decoded picture that has passed through theadaptive loop filter is stored in the memory.

In the embodiment of FIG. 9, it is assumed that the storage unit block910 or 920 includes 16 minimum unit blocks in total, which are arrangedby 4 lines in width and 4 lines in length, that is, in the 4×4 form.Here, each of 16 minimum unit blocks may have one piece of motioninformation, and one storage unit block may have 16 pieces of motioninformation. The storage unit block may be determined as a block havinga predetermined size, or may be determined by the compression ratioinformation transmitted from the encoder. For example, the embodiment ofFIG. 9 may correspond to a case where motion_vector_buffer_comp_ratio is4.

Referring to 910 of FIG. 9, each of the decoded minimum unit blocks mayhave one motion vector and one reference picture index. Further, theminimum unit blocks included in one storage unit block may have separatepieces of motion information.

Referring to 920 of FIG. 9, the encoder and the decoder may select themotion vector (X0, Y0) of the top left block (TL) among the motionvectors in the storage unit block as a representative motion vector forthe current storage unit block. At this time, the selectedrepresentative motion vector may be allocated to all minimum unit blocksin the storage unit block. That is, the selected representative motionvector may be stored in the memory (motion vector buffer) as arepresentative of 16 motion vectors in the current storage unit block.On the other hand, if the current picture is a B picture, the referencepicture of the reference picture list 0 (L0) and the reference pictureof the reference picture list 1 (L1) may be used for the interprediction, and thus motion information for both L0 and 1 may be stored.

If the top left block is encoded and/or decoded in the intra mode, amotion vector may not exist in the top left block. In this case, amotion vector of (0, 0) may be allocated to all minimum unit blocks inthe storage unit block. At this time, the motion vector of (0, 0) may bestored in the memory (motion vector buffer) as a representative of 16motion vectors in the current storage unit block.

According to the above-described temporal motion information compressionmethod, the motion vectors may be stored with low resolution, and thusthe size of the memory for storing the motion vectors may be reduced.However, since the motion vectors of the top left block, that is, themotion vectors in a deflected position, are collectively allocated toall the minimum unit blocks in the storage unit block, coding efficiencymay decrease. Further, in the case where the top left block is coded inthe intra mode, there is a problem in that the motion vector of (0, 0)is stored regardless of whether any block coded in the inter mode existsin the blocks, except in the case of the top left block. Further, in theabove-described temporal motion information compression method, sincethe encoder and the decoder allocate the same motion vector to allminimum unit blocks without considering the reference picture index thatcorresponds to each motion vector in the storage unit block, distortionmay occur.

FIG. 10 is a conceptual diagram explaining another embodiment of amethod for compressing temporal motion information.

FIG. 10 may illustrate one storage unit block. The storage unit blockmay include a plurality of minimum unit blocks. Here, each of theminimum unit blocks may have one piece of motion information. As anembodiment, the size of the minimum unit block may be 4×4, and the sizeof the storage unit block may be 16×16. At this time, the storage unitblock may include 16 minimum unit blocks which are arranged by 4 linesin width and 4 lines in length, that is, in the 4×4 form. The sizes ofthe storage unit block and the minimum unit block are not limited to theabove-described embodiment. The storage unit block may include theminimum unit blocks arranged in an N×N (N being a natural number) form.In FIG. 10, (X0, Y0) to (X15, Y15) represent motion vectors, and ref_idxn (n is an integer that is equal to or larger than 0) representreference picture indexes.

The encoder and the decoder may select a motion vector of apredetermined minimum unit block from among the motion vectors in thestorage unit block as a representative motion vector for the currentstorage unit block. At this time, the encoder and the decoder may selectthe motion vector in the block in an alternative specified position thatis not the top left block, as the representative motion vector.

As an embodiment, the encoder and the decoder may select the motionvector (X3. Y3) of the top right block RT, the motion vector (X12, Y12)of the bottom left block BL, or the motion vector (X15, Y15) of thebottom right block BR as the representative motion vector for thecurrent storage unit block. Further, the encoder and the decoder mayselect the motion vector of the top left center block Center_LT or C0,the motion vector of the top right center block Center_RT or C1, themotion vector of the bottom left center block Center_BL or C2, or themotion vector of the bottom right center block Center_BR or C3 as therepresentative motion vector for the current storage unit block.

The position of the minimum unit block that corresponds to therepresentative motion vector is not limited only to that of theabove-described embodiment, but a motion vector of any minimum unitblock in the storage unit block may be determined as the representativemotion vector that represents the storage unit block. For example, if itis assumed that the position on the x axis of the minimum unit blocksarranged in the 4×4 form is block_x and the position on the y axis isblock_y, the motion vector of any block that corresponds to the positionof (block_x, block_y) (block_x=0, 1, 2, or 3, block_y=0, 1, 2, or 3) maybe determined as the representative motion vector.

As another embodiment, the position of the minimum unit block thatcorresponds to the representative motion vector may be adaptivelydetermined depending on the compression ratio of the motion vector.Here, the compression ratio of the motion vector may be represented bymotion_vector_buffer_comp_ratio.

For example, if motion_vector_buffer_comp_ratio is 4, the motion vectorof the bottom right block may be selected as the representative motionvector for the current storage unit block. Further, ifmotion_vector_buffer_comp_ratio is 8 or 16, the motion vector of thebottom right center block may be selected as the representative motionvector for the current storage unit block. The method for selecting therepresentative motion vector depending on the respective compressionratios is not limited to the above embodiment, but may differ dependingon implementation and/or need.

The position of the selected representative motion vector may correspondto the representative position for storing the motion vector, and therepresentative motion vector may represent the whole storage unit block.That is, the selected representative motion vector may be allocated toall minimum unit blocks in the storage unit block, the selectedrepresentative motion vector may be stored in the memory (motion vectorbuffer) as a representative of all motion vectors in the current storageunit block.

In the above-described embodiments, the explanation has been made aroundthe motion vector. However, the present invention is not limitedthereto, but the above-described embodiments may be applied to generalmotion information. Here, motion information may be a reference pictureindex, prediction mode information (for example, in the prediction mode,L0 prediction, L1 prediction, uni-prediction, and bi-prediction may beprovided), or the like, in addition to the motion vector.

FIG. 11 is a conceptual diagram schematically illustrating still anotherembodiment of a method for compressing temporal motion information. 1110and 1120 of FIG. 11 may indicate storage unit blocks. In FIG. 11, mv_n(n=0, . . . , and 15) represent motion vectors, and ref_m (m=0, . . . ,and 15) represent reference picture indexes. It is assumed that mv_n andref_m are allocated to the minimum unit blocks in a z-scan order.

Referring to 1110 of FIG. 11, the encoder and the decoder may select themotion vector mv_0 of the top left block 1113 from among the motionvectors in the storage unit block as a representative motion vector forthe storage unit block. However, as described later, when the temporalmotion vector predictor is derived, the block located in the bottomright center in a co-located block may be determined as the temporalreference block, and the motion vector of the determined temporalreference block may be determined as the temporal motion vectorpredictor. At this time, it may be inefficient that the motion vectormv_0 of the top left block 1113 is selected as the representative motionvector for the storage unit block. Accordingly, the encoder and thedecoder may select the motion vector mv_12 of the bottom right centerblock 1116 as the representative motion vector for the storage unitblock instead of the motion vector mv_0 of the top left block 1113.

Referring to 1120 of FIG. 11, the position of the selectedrepresentative motion vector mv_12 may correspond to the representativeposition for storing the motion vector, and the representative motionvector may represent the whole storage unit block. That is, the selectedrepresentative motion vector mv_12 may be allocated to all the minimumunit blocks in the storage unit block, and the selected representativemotion vector may be stored in the memory (motion vector buffer) as arepresentative of all motion vectors in the current storage unit block.

FIG. 12 is a conceptual diagram schematically illustrating still anotherembodiment of a method for compressing temporal motion information.

In 1210 and 1220 of FIG. 12, mv_n (n=0, . . . , and 15) represent motionvectors, and ref_m (m=0, . . . , and 15) represent reference pictureindexes. It is assumed that mv_n and ref_m are allocated to the minimumunit blocks in a z-scan order. Further, in 1230 of FIG. 12, (X0, Y0) to(X15, Y15) represent motion vectors, and ref_idx n (n is an integer thatis equal to or larger than 0) represent reference picture indexes.

Referring to 1210 of FIG. 12, the encoder and the decoder may select themotion vector mv_0 of the top left block among the motion vectors in thestorage unit block as a representative motion vector for the storageunit block. The selected representative motion vector mv_0 may beallocated to all the minimum unit blocks in the storage unit block, andthe selected representative motion vector may be stored in the memory(motion vector buffer) as a representative of all motion vectors in thecurrent storage unit block.

In 1210 of FIG. 12, the encoder and the decoder allocate the same motionvector to all of the minimum unit blocks without consideration for thereference picture indexes that correspond to the respective motionvectors in the storage unit block. At this time, only the motion vectormemory may be compressed without changing the reference picture indexmemory. Accordingly, inconsistency may occur between the motion vectorand the reference picture index, thereby causing distortion. Suchinconsistency may reduce the accuracy of the temporal motion vectorpredictor and lower the performance of motion vector scaling.Accordingly, in order to reduce the size of the memory allocated for thereference picture index and to improve coding efficiency, a method forcompressing the temporal motion information that compresses thereference picture index memory together with the motion vectors may beprovided.

Referring to 1220 of FIG. 12, in the same manner as 1210, the encoderand the decoder may select the motion vector mv_0 of the top left blockfrom among the motion vectors in the storage unit block as arepresentative motion vector for the storage unit block. Further, theencoder and the decoder may select the reference picture index ref_0 ofthe top left block from among the reference picture indexes in thestorage unit block as a representative reference picture index for thestorage unit block. That is, the encoder and the decoder may select thereference picture index that the minimum unit block corresponding to therepresentative motion vector has as the representative reference pictureindex, and the reference picture index may be compressed in the samemethod as that used for the motion vector.

The selected representative motion vector mv_0 and representativereference picture index ref_0 may be allocated to all the minimum unitblocks in the storage unit block, and the selected representative motionvector and representative reference picture index may be stored in thememory as the representatives of all the motion vectors and all therepresentative reference picture indexes in the current storage unitblock.

Referring to 1230 of FIG. 12, the encoder and the decoder may select themotion vector (X0, Y0) and the reference picture index ref_idx_2 in thetop left block as the representative motion vector and therepresentative reference picture index for the storage unit block. Theselected representative motion vector and representative referencepicture index may be allocated to all the minimum unit blocks in thestorage unit block, and the selected representative motion vector andrepresentative reference picture index may be stored in the memory asthe representatives of all the motion vectors and all the representativereference picture indexes in the storage unit block.

In the above-described 1220 and 1230, since both the motion vector andthe reference picture index are compressed and stored, the distortionmay be reduced. Further, the embodiment of 1220 and 1230 may be appliedin combination with the above-described embodiments in FIGS. 9 to 11.That is, even in the embodiments of FIGS. 9 to 11, the reference pictureindex that the minimum unit block corresponding to the representativemotion vector has may be selected as the reference picture index, andthe reference picture index may be compressed in the same manner as themotion vector.

FIG. 13 is a conceptual diagram schematically illustrating still anotherembodiment of a method for compressing temporal motion information.

In the above-described embodiments in FIGS. 9 to 12, the minimum unitblock that is selected to derive the representative motion informationthat represents the storage unit block may not include available motioninformation. The case where the minimum unit block does not include theavailable motion information may be resulting from the case where theminimum unit block is unavailable, the case where the minimum unit blockis coded in the intra mode, or the case where there is not an availablemotion vector in the reference picture list (for example, referencepicture list 0 and reference picture list 1) that corresponds to theminimum unit block.

In the case where the minimum unit block that is selected to derive therepresentative motion information does not include the available motioninformation, as described above with reference to FIG. 9, the encoderand the decoder may store the motion vector of (0, 0) in the memory asthe representative of all the motion vectors in the storage unit block.However, if the selected minimum unit block does not include theavailable motion information, there may be a problem in that the motionvector of (0, 0) is allocated to all the minimum unit blocks even in thecase where the available block or the block coded in the inter modeexists in the storage unit block. Accordingly, a method for compressingthe temporal motion information to select the minimum unit block havingthe available motion information and to determine the representativemotion information may be provided.

As an embodiment, the encoder and the decoder may check whether theminimum unit block being scanned has the available motion informationwhile scanning the minimum unit blocks in the storage unit block in thepredetermined order. At this time, the encoder and the decoder mayselect the motion information of the block that has the fastest scanningorder from among the minimum unit blocks having the available motioninformation as the representative motion information of the storage unitblock. That is, the encoder and the decoder may perform scanning on theminimum unit blocks until the encoder and the decoder find the minimumunit block having the available motion information.

Further, in the scanning process, the encoder and the decoder may checknot only whether the minimum unit block has the available motioninformation (for example, whether the minimum unit block is coded in theinter mode) but also whether the reference picture index value that theminimum unit block has is 0. At this time, the encoder and the decodermay select the motion information of the first minimum unit block (theminimum unit block having the highest scanning priority) that satisfiesthe above condition as the representative motion information of thestorage unit block by performing scanning on the minimum unit blocksuntil the minimum unit block that satisfies the above condition isfound.

The position of the representative motion information selected by theabove-described method may correspond to the representative position forstoring the motion information, and the representative motioninformation may represent the entire storage unit blocks. That is, theselected representative motion information may be allocated to all theminimum unit blocks in the storage unit block, and the selectedrepresentative motion information may be stored in the memory as therepresentative of all pieces of motion information in the currentstorage unit block. For example, in the case where it is also checkedwhether the reference picture index value that the minimum unit blockhas is 0 in the scanning process, the reference picture index value of 0may be stored in the memory as the representative of all the referencepicture indexes in the current storage unit block.

The minimum unit block that is targeted for scanning and the scanningorder may be diversely determined. In FIG. 13, the number indicated onthe minimum unit block in each storage unit block represents thescanning order.

Referring to 1310 of FIG. 13, the encoder and the decoder may scan allthe minimum unit blocks in the storage unit block. As an embodiment, asillustrated as 1313 in FIG. 13, the scanning order may be a rasterscanning order. Further, as illustrated by 1316 and 1319 of FIG. 13, theencoder and the decoder may perform the scanning, starting from theneighboring blocks in the center of the storage unit blocks toward theboundary of the storage unit block.

In order to reduce the amount of computation and the complexity, theencoder and the decoder may scan only a limited number of blocks fromamong the minimum unit blocks in the storage unit block. As anembodiment, as illustrated by 1320 in FIG. 13, the encoder and thedecoder may scan only the top left center block, the top right centerblock, the bottom left center block, and the bottom right center blockin the predetermined order. Further, as illustrated as 1330 in FIG. 13,the encoder and the decoder may scan only the top left block, the topright block, the bottom left block and the bottom right block in thepredetermined order.

The above-described embodiment may be applied to the motion vector.However, the application of the above-described embodiment is notlimited thereto, and the above-described embodiment may be applied toall pieces of motion information. Here, the motion information may bethe motion vector and the reference picture index. For example, thereference picture index, which the minimum unit block corresponding tothe representative motion vector has, may be selected as therepresentative reference picture index, and the reference picture indexmay be compressed in the same manner as the motion vector.

FIG. 14 is a conceptual diagram schematically illustrating still anotherembodiment of a method for compressing temporal motion information. Inthe embodiment of FIG. 14, it is assumed that the motion vector of thebottom right center block in the storage unit block is selected as therepresentative motion vector.

If the minimum unit block that is selected to derive the representativemotion information does not include the available motion information,the encoder and the decoder may store the motion vector of (0, 0) in thememory as the representative of all the motion vectors in the storageunit block. However, the problem as described above with reference toFIG. 13 may occur.

Referring to 1410 of FIG. 14, the bottom right center block 1415 is ablock that is coded in the intra mode. Accordingly, the bottom rightcenter block 1415 may not include the available motion information. Atthis time, the motion vector of (0, 0) may be stored in the memory asthe representative of all the motion vectors. However, although theminimum unit block having the available motion information exists in thestorage unit block, the motion vector of (0, 0) is allocated to all theminimum unit blocks to cause the problem that the coding efficiencydeteriorates. Accordingly, the minimum unit block having the availablemotion information instead of the motion vector of (0, 0) may be used tocompress the motion information.

In order to solve the above-described problem, the encoder and thedecoder may check whether the minimum unit block being scanned has theavailable motion information while scanning the minimum unit blocks inthe storage unit block in the predetermined order. For example, theencoder and the decoder may scan 4 minimum unit blocks in the order ofthe bottom right center block, the top left center block, the top rightcenter block, and the bottom left center block. At this time, theencoder and the decoder may select the motion information of the blockhaving the fastest scanning order among the minimum unit blocks havingthe available motion information as the representative motioninformation of the storage unit block. That is, the encoder and thedecoder may perform the scanning until the minimum unit block having theavailable motion information is found.

Referring to 1420 of FIG. 14, the bottom right center block is a blockthat is coded in the intra mode and thus may not include the availablemotion information. Accordingly, the encoder and the decoder may selectthe motion vector mv_3 of the top left center block 1425 that is locatednext to the bottom right center block in the scanning order as therepresentative motion vector of the current storage unit block.

Referring to 1430 of FIG. 14, the position of the selectedrepresentative motion vector mv_3 may correspond to the representativeposition to store the motion vector, and the representative motionvector may represent the entirety of the storage unit blocks. That is,the selected representative motion vector mv_3 may be allocated to allthe minimum unit blocks in the storage unit block, and the selectedrepresentative motion vector may be stored in the memory (motion vectorbuffer) as the representative of all the motion vectors in the currentstorage unit block.

FIG. 15 is a conceptual diagram schematically illustrating still anotherembodiment of a method for compressing temporal motion information. FIG.15 illustrates a storage unit block 1510 and neighboring blocks of thestorage unit block 1510. The neighboring blocks may include blocks 1, 2,3, 4, 6, 7, 8, 9, 11, 12, 13, 14, 16, 17, 18, and 19 that are adjacentto the storage unit block 1510 and blocks 0, 5, 10, and 15 that arelocated at outer corners of the storage unit block 1510. Hereinafter, inthe embodiment of FIG. 15, the neighboring blocks may mean theneighboring blocks of the storage unit block 1510.

In the above-described embodiments in FIGS. 9 to 14, the minimum unitblock, which is selected by the encoder and the decoder to derive therepresentative motion information that represents the storage unit block1510, may not include available motion information. In this case, as aresult, the motion vector of (0, 0) may be stored in the memory as therepresentative of all the motion vectors. The case where the minimumunit block does not include the available motion information may be thecase where the minimum unit block is unavailable, the case where theminimum unit block is coded in the intra mode, or the case where thereis not an available motion vector in the reference picture list (forexample, reference picture list 0 and reference picture list 1) thatcorresponds to the minimum unit block or the motion vector in thereference picture list is unavailable.

For example, if the top left block in the storage unit block is coded inthe intra mode in the embodiment of FIG. 9, the top left block may notinclude the available motion information. Further, in the embodiments ofFIGS. 10 to 12, the minimum unit block that is selected by the encoderand the decoder may not include the available motion information.Further, in the embodiments of FIGS. 13 and 14, all the minimum unitblocks scanned by the encoder and the decoder may not include theavailable motion information.

In the above-described cases, the encoder and the decoder may determinethe representative motion vector for the current storage unit blockusing the motion information of the neighboring blocks instead ofselecting the motion vector of (0, 0) as the representative motionvector.

As one embodiment, it is assumed that only one block among theneighboring blocks of the storage unit block 1510 has the availablemotion information. At this time, the encoder and the decoder may usethe motion information of the neighboring block having the availablemotion information as the representative motion information of thecurrent storage unit block 1510.

As another embodiment, it is assumed that two or more blocks among theneighboring blocks of the storage unit block 1510 have the availablemotion information.

At this time, as one embodiment, the encoder and the decoder may use thefirst neighboring block having the reference picture index of 0 as therepresentative motion information of the current storage unit block 1510while scanning the neighboring blocks in the order of the numbersallocated to the neighboring blocks. Here, the scanning order is notlimited to the order illustrated in FIG. 15, and may differ depending onimplementation and/or need.

As another embodiment, the encoder and the decoder may obtain the medianvalue of the motion information (for example, motion vector) value ofthe neighboring block, and then use the median value as therepresentative motion information of the current storage unit block1510. At this time, the neighboring blocks that do not include theavailable motion information may be excluded without having been usedwhen the median value is derived. Further, the encoder and the decodermay allocate a predetermined motion vector value to the neighboringblocks that do not include the available motion information, and derivethe median value using both the neighboring block to which thepredetermined motion information value is allocated and the neighboringblock including the available motion information. As an embodiment, themotion vector of (0, 0) may be allocated to the neighboring blocks thatdo not include the available motion information, and the motion vectorof (0, 0) may be used to derive the median value.

As another embodiment, the encoder and the decoder may determine therepresentative motion information of the storage unit block 1510 basedon a pixel difference value between the pixel of the storage unit block1510 and the pixel of the neighboring block.

For example, in the case of a block No. 0, the final pixel differencevalue that is derived by a difference in pixel value between the bottomrightmost pixel of the block No. 1 and the top leftmost pixel of thestorage unit block 1510 may be used to determine the representativemotion information. In the case of a block No. 5, the final pixeldifference value that is derived by a difference in pixel value betweenthe bottom leftmost pixel of the block No. 5 and the top rightmost pixelof the storage unit block 1510 may be used to determine therepresentative motion information. Further, in the case of a block No.10, the final pixel difference value that is derived by a difference inpixel value between the top leftmost pixel of the block No. 10 and thebottom rightmost pixel of the storage unit block 1510 may be used todetermine the representative motion information. In the case of a blockNo. 15, the final pixel difference value that is derived by a differencein pixel value between the top rightmost pixel of the block No. 15 andthe bottom leftmost pixel of the storage unit block 1510 may be used todetermine the representative motion information.

Further, even in the case of a block No. 1, 2, 3, 4, 6, 7, 8, 9, 11, 12,13, 14, 16, 17, 18, or 19, the final pixel difference value that is usedto determine each of the representative motion information may bederived. Here, a boundary between the block No. N (where, N is 1, 2, 3,4, 6, 7, 8, 9, 11, 12, 13, 14, 16, 17, 18, or 19) and the storage unitblock 1510 is called a boundary No. N. At this time, a difference valuebetween the sum of pixel values of M (where, M is a positive integer,for example, 4, 8, 16, or 32) pixels that are located nearest to theboundary No. N of the pixel in the block No. N and the sum of pixelvalues of M pixels which are located nearest to the boundary No. N amongthe pixels in the storage unit block 1510 may be obtained. The encoderand the decoder may derive an average difference value by dividing theobtained difference value by M, and use the obtained difference value asthe final pixel difference value of the block No. N.

If the final pixel difference value from the storage unit block 1510 isobtained with respect to the respective neighboring blocks in theabove-described method, the encoder and the decoder may determine themotion information of the block having the smallest final pixeldifference value from among the neighboring blocks as the representativemotion information of the current storage unit block 1510. If there area plurality of blocks having identical smallest final pixel differencevalues and/or if the neighboring blocks have the same final pixeldifference value, the encoder and the decoder may determine the motioninformation of the neighboring block having the smallest allocatednumber in FIG. 15 as the representative motion information of thecurrent storage unit block 1510.

As another embodiment, all the neighboring blocks of the storage unitblock 1510 may not have the available motion information. At this time,the encoder and the decoder may select the motion vector of (0, 0) asthe representative motion vector.

If the representative motion information is determined, the selectedrepresentative motion information may be allocated to all the minimumunit blocks in the storage unit block 1510. Accordingly, the selectedrepresentative motion information may be stored in the memory as therepresentative of all pieces of motion information in the currentstorage unit block 1510.

The above-described embodiment may be applied to the motion vector.However, the application of the above-described embodiment is notlimited thereto, but the above-described embodiment may be applied toall pieces of motion information. Here, the motion information may bethe motion vector and the reference picture index. For example, thereference picture index, which the minimum unit block corresponding tothe representative motion vector has, may be selected as therepresentative reference picture index, and the reference picture indexmay be compressed in the same manner as the motion vector.

On the other hand, as described above, in the case where the motionvector prediction is performed, the temporal motion vector predictor(TMVP) may be used as a motion vector predictor candidate. The temporalmotion vector predictor may be obtained from the motion vector of the“temporal reference block” in the reference picture. Here, the temporalreference block may mean the storage unit block in the referencepicture, which includes the motion vector that is used as the temporalmotion vector predictor. The temporal reference block may be derivedbased on the current block, and/or the “co-located block” of therespective reference pictures, which is the block co-located with thecurrent block. Hereinafter, in embodiments to be described later, thecurrent block means a prediction target block in the current picture,and the current block may correspond to, for example, a prediction unit(PU).

The wording indicating the positions of the minimum unit blocks in thestorage unit block (the top left block, top right block, bottom leftblock, bottom right block, top left center block, top right centerblock, bottom left center block, and bottom right center block) asdescribed above with reference to FIG. 7 may be used as wordingindicating the positions of the storage unit blocks in the current blockand/or the co-located block. In the embodiment of FIG. 16, the wordingused to refer to the positions of the storage unit blocks in theco-located block will be defined.

FIG. 16 is a conceptual diagram schematically illustrating a co-locatedblock included in a reference picture. FIG. 16 illustrates a co-locatedblock 1600 for the current block. Respective blocks that constitute theco-located block 1600 may represent the storage unit blocks. That is,the respective blocks in the co-located block may represent a unit inwhich the motion information is compressed and stored, and one piece ofmotion information may be stored in each block in the co-located block.As an embodiment, the size of the storage unit block may be 16×16.

As described above, the co-located block 1600 may mean the block in thereference picture, which is located in the same position as the currentblock. It is defined that the position of the top leftmost pixel in thecurrent block and the co-located block 1600 is (xP, yP), and the widthand the height of the current block and the co-located block 1600 aredefined as variables of nPSW and NPSH, respectively.

Hereinafter, in the embodiment of the present invention, the wording isdefined in a manner wherein a storage unit block including pixelsexisting in (xP, yP), that is, a storage unit block located on the topleft side of the co-located block 1600, is a top left block 1610, astorage unit block including pixels existing in (xP+nPSW−1, yP), thatis, a storage unit block located on the top right side of the co-locatedblock 1600, is a top right block 1620, a storage unit block includingpixels existing in (xP, yP+nPSH−1), that is, a storage unit blocklocated on the bottom left side of the co-located block 1600, is abottom left block 1630, and a storage unit block including pixelsexisting in (xP+nPSW−1, yP+nPSH−1), that is, a storage unit blocklocated on the bottom right side of the co-located block 1600, is abottom right block 1640. Further, a storage unit block including pixelsexisting in (xP+nPSW, yP+nPSH), that is, a storage unit block located onthe bottom right corner of the co-located block 1600, is defined as abottom right corner block 1650.

Further, the wording is defined in a manner wherein a storage unit blockincluding pixels existing in (xP+nPSW/2−1, yP+nPSH/2−1), that is, astorage unit block located in the top left center of the co-locatedblock 1600, is a top left center block 1660, a storage unit blockincluding pixels existing in (xP+nPSW/2, yP+nPSH/2−1), that is, astorage unit block located in the top right center of the co-locatedblock 1600, is a top right center block 1670, a storage unit blockincluding pixels existing in (xP+nPSW/2−1, yP+nPSH/2), that is, astorage unit block located in the bottom left center of the co-locatedblock 1600, is a bottom left center block 1680, and a storage unit blockincluding pixels existing in (xP+nPSW/2, yP+nPSH/2), that is, a storageunit block located in the bottom right center of the co-located block1600, is a bottom right center block 1690.

Here, as described above, the respective blocks (the top left block1610, the top right block 1620, the bottom left block 1630, the bottomright block 1640, the bottom right corner block 1650, the top leftcenter block 1660, the opt right center block 1670, the bottom leftcenter block 1680, and the bottom right center block 1690) may bespecified by coordinates of the pixels included therein. For example,the bottom right center block 1690 may be specified by (xP+nPSW/2,yP+nPSH/2).

In the above-described embodiment, the respective blocks are describedbased on the co-located block. However, since the current block and theco-located block in the reference picture occupy the same specialposition, the above-described pixel coordinates and wording can also beapplied to the current block. Hereinafter, in the following embodiments,the position of the storage unit block is described based on theco-located block. However, the position of the storage unit block may bedetermined in the same manner based on the current block.

On the other hand, the encoder and the decoder may select a block in apredetermined position in the reference picture and/or in a positiondetermined by a predetermined process as a temporal reference block forthe current block. Here, the position of the temporal reference blockmay be determined based on the current block and/or the co-locatedblock. The encoder and the decoder may derive the motion vector of theselected temporal reference block and determine the derived motionvector as the temporal motion vector predictor. At this time, since thetemporal reference block corresponds to the storage unit, the encoderand the decoder may derive the temporal motion information predictorfrom the prediction unit having the same motion information as thetemporal reference block.

Since the temporal reference block can represent one storage unit, asdescribed above with reference to FIG. 16, the temporal reference blockmay be specified by the coordinates of the pixel included in thetemporal reference block. For example, if the bottom right center blockis determined as the temporal reference block, the temporal referenceblock may be specified by (xP+nPSW/2, yP+nPSH/2).

On the other hand, since the temporal reference block can represent onestorage unit, a minimum unit block in which the representative motioninformation is stored may exist in the temporal reference block. Asdescribed above with reference to FIG. 7, the position in which therepresentative motion information is stored may be specified by thecoordinates of the pixel included in the minimum unit block. Forexample, it is assumed that the size of the storage unit block is 16×16and the motion information of the minimum unit block that is located onthe top left side in the storage unit block is used as therepresentative motion information. At this time, if the coordinates ofthe pixel for specifying the temporal reference block are (xPCtr,yPCtr), the position of the representative motion information may bespecified by ((xPCtr>>4)<<4, (yPCtr>>4)<<4).

At this time, a prediction unit that covers the coordinates where therepresentative motion information is specified may exist in thereference picture. In the embodiment of the present invention, theprediction unit is called colPu. Since the motion information of colPuis equal to the motion information of the selected temporal referenceblock, the encoder and the decoder may copy and use the motion vector ofcolPu as the temporal motion vector predictor of the current block.

Hereinafter, embodiments of the method for deriving the temporal motionvector predictor will be described, and the above-described contents maybe applied to the methods for deriving the temporal motion vectorpredictor to be described later. Further, for convenience inexplanation, it is assumed that the size of the storage unit of themotion vector, that is, the size of the storage unit block, is 16×16.

FIG. 17 is a conceptual diagram schematically illustrating an embodimentof a method for deriving a temporal motion vector predictor.

Referring to 1710 of FIG. 17, the current picture 1730 may represent thecurrent encoding/decoding target picture, and may include the currentblock 1740. The temporal motion vector predictor for the current block1740 may be derived from the temporal reference block in the referencepicture 1750.

As an embodiment, the encoder and the decoder may select the top leftcenter block 1770 in the co-located block 1760 as the temporal referenceblock for the current block 1740. At this time, the motion vector of thedetermined temporal reference block may be determined as the temporalmotion vector predictor for the current block 1740.

However, in this case, the temporal reference block, which is selectedto derive the temporal motion vector predictor, may not includeavailable motion information. The case where the temporal referenceblock does not include the available motion information may be the casewhere the temporal reference block is unavailable or the case where thetemporal reference block is coded in the intra mode.

If the temporal reference block, which is selected to derive thetemporal motion vector predictor, does not include the available motioninformation, the encoder and the decoder may determine the motion vectorof (0, 0) as the temporal motion vector predictor. However, in thiscase, even if the available block or the block coded in the inter modeexists in the co-located block 1760, the motion vector of (0, 0) may bedetermined as the temporal motion vector predictor, and the problem thatinaccurate motion information is used may occur.

Referring to 1720 of FIG. 17, the top left center block 1770 in theco-located block 1760 may be a block coded in the intra mode, and thetop right center block 1780 may be a block which is coded in the intermode and includes available motion information. At this time, if the topleft center block 1770 is selected as the temporal reference block, thetop left center block 1770 does not include the available motioninformation, and thus the motion vector of (0, 0) may be determined asthe temporal motion vector predictor. However, since the motion vectorof (0, 0) may be inaccurate motion information and the available motioninformation is stored in the top right center block 1780, the encoderand the decoder may not use the motion vector of (0, 0) that is theinaccurate motion information as the temporal motion vector predictor.

FIG. 18 is a conceptual diagram schematically illustrating an embodimentof a temporal reference block in which a temporal motion vectorpredictor may be located. FIG. 18 illustrates a block 1810 which appearswhen the current block and the co-located block overlap each other.

Referring to FIG. 18, the temporal reference block, from which thetemporal motion vector predictor is derived, may be a top left centerblock (C0) 1820, a bottom right center block (C3) 1830, a bottom rightblock (BR) 1840, or a bottom right corner block (H) 1850.

Further, blocks located in an area indicated by X may be selected as thetemporal reference blocks in which the temporal motion vector predictoris located. The block located in the area indicated by X may be a topleft block 1861, a top right block 1863, a bottom left block 1865, a topright center block 1867, or a bottom left center block 1869.

FIG. 19 is a conceptual diagram schematically illustrating anotherembodiment of a method for deriving a temporal motion vector predictor.

Here, 1910, 1920, and 1930 of FIG. 19 illustrate co-located blocks forthe current block, respectively. As described above, the co-locatedblock may mean a block in a reference picture, that is in the sameposition as the current block. Further, respective blocks thatconstitute the co-located block may represent the storage unit blocks.That is, the respective blocks in the co-located block may represent theunit in which the motion information is compressed and stored, and onepiece of motion information may be stored in each block in theco-located block. As described above with reference to FIG. 8, the sizeof the storage unit block may be determined as a predetermined size, andmay be derived using the compression information transmitted from theencoder. At this time, the compression information may be included in aSequence Parameter Set (SPS), a Picture Parameter Set (PPS), or a sliceheader to be transmitted from the encoder to the decoder. In theembodiment of FIG. 19, it is assumed that the size of the storage unitof the motion vector, that is, the size of the storage unit block, is16×16.

As described above, the encoder and the decoder may select the block inthe specified position in the co-located block as the temporal referenceblock for the current block. The encoder and the decoder may derive themotion vector of the selected temporal reference block, and determinethe derived motion vector as the temporal motion vector predictor.

On the other hand, 1910 of FIG. 19 illustrates the co-located block inthe case where the size of the current block is 64×64. Referring to 1910of FIG. 19, as an example, the block in the predetermined position thatis selected to derive the temporal motion vector predictor may be thetop left center block (block No. 0) of the co-located block. That is,the encoder and the decoder may select the top left center block (blockNo. 0) as the temporal reference block for the current block. In thiscase, the motion vector of the top left center block (block No. 0) maybe used as the temporal motion vector predictor.

As another example, the block in the predetermined position that isselected to derive the temporal motion vector predictor may be the topright center block (block No. 1) of the co-located block. At this time,the encoder and the decoder may select the top right center block (blockNo. 1) as the temporal reference block for the current block. As stillanother example, the block in the predetermined position that isselected to derive the temporal motion vector predictor may be thebottom left center block (block No. 2) of the co-located block. At thistime, the encoder and the decoder may select the bottom left centerblock (block No. 2) as the temporal reference block for the currentblock. Further, as still another example, the block in the predeterminedposition that is selected to derive the temporal motion vector predictormay be the bottom right center block (block No. 3) of the co-locatedblock. At this time, the encoder and the decoder may select the bottomright center block (block No. 3) as the temporal reference block for thecurrent block. In the above-described examples, the motion vector of theselected temporal reference block may be used as the temporal motionvector predictor for the current block.

As one embodiment, it is assumed that the bottom right center block(block No. 3) is used as the temporal reference block and the motioninformation of the minimum unit block that is located in the bottomright center in the storage unit block is used as the representativemotion information. At this time, a detailed embodiment of a method forguiding colPu is as follows.

The encoder and the decoder may select the bottom right center block inthe co-located block as the temporal reference block. At this time, theposition of the temporal reference block may be specified by thecoordinates of the pixels included in the current block and theco-located block, and the bottom right center block may be specified by(xP+(nPSW>>1), yP+(nPSW>>1)). This may be represented as follows.

-   -   Variable colPu and its position (xPCol, yPCol) are derived in        the following ordered steps:        -   Bottom-right center luma position of the current prediction            unit is defined by            xPCtr=xP+(nPSW>>1)            yPCtr=yP+(nPSH>>1)

Here, xPCtr and yPCtr may represent the coordinates specified by thetemporal reference block. xP and yP may represent the coordinates of thetop leftmost pixel in the current block, mPSW may represent the width ofthe current block, and nPSH may represent the height of the currentblock.

If the temporal reference block is specified, the encoder and thedecoder may specify the position of the minimum unit block in which therepresentative motion vector in the temporal reference block is stored.At this time, the position of the minimum unit block may be specified by((xPCtr>>4)<<4+8, (yPCtr>>4)<<4+8). At this time, colPu may be specifiedby the prediction unit in the reference picture, which includes thecoordinates of ((xPCtr>>4)<<4+8, (yPCtr>>4)<<4+8). This may berepresented as follows.

-   -   The variable colPu is set as the prediction unit covering the        modified position given by ((xPCtr>>4)<<4+8, (yPCtr>>4)<<4+8)        inside the colPic.

At this time, the top leftmost coordinates in colPu may be representedby (xPCol, xPCol) as follows.

-   -   (xPCol, yPCol) is set equal to the top-left luma sample of the        colPu relative to the top-left luma sample of the colPic.

Further, 1920 of FIG. 19 illustrates the co-located block in the casewhere the size of the current block is 64×32. In 1920 of FIG. 19, thetemporal motion vector predictor for the current block may be derived ina method that is identical or similar to 1910 of FIG. 19.

As an example, the block in the predetermined position that is selectedto drive the temporal motion vector predictor may be the top left centerblock (block No. 0) of the co-located block. At this time, the encoderand the decoder may select the top left center block (block No. 0) asthe temporal reference block for the current block. As another example,the block in the predetermined position that is selected to drive thetemporal motion vector predictor may be the top right center block(block No. 1) of the co-located block. At this time, the encoder and thedecoder may select the top right center block (block No. 1) as thetemporal reference block for the current block. As still anotherexample, the block in the predetermined position that is selected todrive the temporal motion vector predictor may be the bottom left centerblock (block No. 2) of the co-located block. At this time, the encoderand the decoder may select the bottom left center block (block No. 2) asthe temporal reference block for the current block. As still anotherexample, the block in the predetermined position that is selected todrive the temporal motion vector predictor may be the bottom rightcenter block (block No. 3) of the co-located block. At this time, theencoder and the decoder may select the bottom right center block (blockNo. 3) as the temporal reference block for the current block. In theabove-described examples, the motion vector of the selected temporalreference block may be used as the temporal motion vector predictor forthe current block.

Further, 1930 of FIG. 19 illustrates the co-located block in the casewhere the size of the current block is 64×64. Referring to 1930 of FIG.19, as an example, the block in the predetermined position that isselected to derive the temporal motion vector predictor may be the topleft block (block No. 4) of the co-located block. That is, the encoderand the decoder may select the top left block (block No. 4) as thetemporal reference block for the current block. In this case, the motionvector of the top left block (block No. 4) may be used as the temporalmotion vector predictor.

As another example, the block in the predetermined position that isselected to derive the temporal motion vector predictor may be thebottom right block (block No. 5) of the co-located block. At this time,the encoder and the decoder may select the bottom right block (block No.5) as the temporal reference block for the current block. In this case,the motion vector of the bottom right block (block No. 5) may be used asthe temporal motion vector predictor.

As an embodiment, it is assumed that the bottom right block (block No.5) is used as the temporal reference block and the motion information ofthe minimum unit block that is located on the bottom right side in thestorage unit block is used as the representative motion information. Atthis time, a detailed embodiment of a method for guiding colPu is asfollows.

The encoder and the decoder may select the bottom right block in theco-located block as the temporal reference block. At this time, theposition of the temporal reference block may be specified by thecoordinates of the pixels included in the current block and theco-located block, and the bottom right block may be specified by(xP+nPSW−1, yP+nPSW−1). This may be represented as follows.

-   -   Variable colPu and its position (xPCol, yPCol) are derived in        the following ordered steps:        -   Right-bottom luma position within the current prediction            unit is defined by            xPRb=xP+nPSW−1            yPRb=yP+nPSH−1

Here, xPRb and yPRb may represent the coordinates specified by thetemporal reference block.

If the temporal reference block is specified, the encoder and thedecoder may specify the position of the minimum unit block in which therepresentative motion vector in the temporal reference block is stored.At this time, the position of the minimum unit block may be specified by((xPRb>>4)<<4+12, (yPRb>>4)<<4+12). At this time, colPu may be specifiedby the prediction unit in the reference picture, which includes thecoordinates of ((xPRb>>4)<<4+12, (yPRb>>4)<<4+12). This may berepresented as follows.

-   -   The variable colPu is set as the prediction unit covering the        modified position given by ((xPRb>>4)<<4+12, (yPRb>>4)<<4+12)        inside the colPic.

At this time, the top leftmost coordinates in colPu may be representedby (xPCol, xPCol) as follows.

-   -   (xPCol, yPCol) is set equal to the top-left luma sample of the        colPu relative to the top-left luma sample of the colPic.

FIG. 20 is a conceptual diagram schematically illustrating still anotherembodiment of a method for deriving a temporal motion vector predictorReferring to FIG. 20, the current picture 2010 represents the currentencoding/decoding picture, and the current picture 2010 may include thecurrent block 2020. The temporal motion vector predictor for the currentblock 2020 may be derived from the reference picture 2030.

Respective blocks constituting the reference picture 2030 may representthe storage unit blocks. That is, the respective blocks constituting thereference picture 2030 may represent a unit in which the motioninformation is compressed and stored, and one piece of motioninformation may be stored in each block constituting the referencepicture 2030. As an example, the size of the storage unit block may be16×16.

The reference picture 2030 may include a co-located block 2040 for thecurrent block. The encoder and the decoder may select the storage unitblock in the predetermined position in the co-located block 2040 as thetemporal reference block for the current block 2020, and the position ofthe temporal reference block may correspond to the position of thetemporal motion vector predictor for the current block 2020.

As an embodiment, the block in the predetermined position that isselected to drive the temporal motion vector predictor may be the topleft center block 2050 of the co-located block 2040. That is, theencoder and the decoder may select the top left center block 2050 as thetemporal reference block for the current block 2020. In this case, themotion vector of the top left center block 2050 may be used as thetemporal motion vector predictor for the current block 2020.

As another example, the block in the predetermined position that isselected to drive the temporal motion vector predictor may be the bottomright center block 2060 of the co-located block 2040 rather than the topleft center block 2050. That is, the encoder and the decoder may selectthe bottom right center block 2060 as the temporal reference block forthe current block 2020. In this case, the motion vector of the bottomright center block 2060 may be used as the temporal motion vectorpredictor for the current block 2020.

FIG. 21 is a conceptual diagram schematically illustrating still anotherembodiment of a method for deriving a temporal motion vector predictor.2110 and 2120 of FIG. 21 illustrate blocks which appear when the currentblock and the co-located block overlap each other.

In FIG. 21, respective blocks constituting the co-located block mayrepresent the storage unit blocks. That is, the respective blocksconstituting the co-located block may represent a unit in which themotion information is compressed and stored, and one piece of motioninformation may be stored in each block in the co-located block. In anembodiment of FIG. 21, for convenience of explanation, it is assumedthat the size of the storage unit of the motion information, that is,the size of the storage unit block, is 16×16, and the size of thecurrent block and the co-located block is 64×64.

As described above in the embodiments of FIGS. 17 to 20, the encoder andthe decoder may select the block in the predetermined fixed position asthe temporal reference block, and in this case, the motion vector of theselected temporal reference block may be used as the temporal motionvector predictor. However, in the embodiments of FIGS. 17 to 20 asdescribed above, the temporal reference block that is selected to derivethe temporal motion vector predictor may not include the availablemotion information. The case where the temporal reference block does notinclude the available motion information may be the case where thetemporal reference block is coded in the intra mode or the case where anavailable motion vector does not exist in the reference picture listthat corresponds to the temporal reference block.

As described above with reference to FIG. 9, even if the temporalreference block does not include the available motion information, themotion vector of (0, 0) may be stored in the memory with respect to thetemporal reference block. At this time, the encoder and the decoder maydetermine the motion vector of (0, 0) as the temporal motion vectorpredictor. However, in this case, even if the storage unit block inwhich the available motion information is stored exists in theco-located block, the motion vector of (0, 0) may be determined as thetemporal motion vector predictor, and the problem that inaccurate motioninformation is used may occur. Accordingly, a method for deriving atemporal motion vector predictor, which determines the temporal motionvector predictor by selecting the temporal reference block havingavailable motion information, may be provided.

As one embodiment, the encoder and the decoder may scan in apredetermined order a plurality of storage unit blocks (hereinafterreferred to as temporal reference block candidates. Since the motionvector of the temporal reference block can be used as the temporalmotion vector predictor, the temporal reference block candidate may becalled a motion vector predictor candidate) in the co-located block, andmay check whether the scanned storage unit block has the availablemotion information (for example, whether the temporal reference blockcandidate is a block coded in the intra mode or whether an availablemotion vector exists in the reference picture list that corresponds tothe temporal reference block candidate). At this time, the encoder andthe decoder may select the candidate having the fastest scanning orderfrom among the temporal reference block candidates having the availablemotion information, as the temporal reference block for the currentblock, and use the motion vector of the selected block as the temporalmotion vector predictor. That is, the encoder and the decoder mayperform scanning until the temporal reference block candidate having theavailable motion information is found, and determine the motion vectorof the first temporal reference block candidate that satisfies theabove-described condition as the temporal motion vector predictor forthe current block.

If all of the temporal reference block candidates which are targeted forscanning do not include the available motion information (for example,if all the temporal reference block candidates are coded in the intramode or are unavailable), the encoder and the decoder may determine thefirst temporal reference block candidate (the temporal reference blockcandidate having the highest scanning priority) in the scanning order asthe temporal reference block for the current block. At this time, as anexample, the motion vector of (0, 0) may be stored in the selectedtemporal reference block, and the motion vector of (0, 0) may be used asthe temporal motion vector predictor.

The temporal reference block candidates and the scanning order may bediversely determined. The numbers marked on the respective storage unitblocks in FIG. 21 may represent the scanning order.

Referring to 2110 of FIG. 21, the encoder and the decoder may use 4blocks among the storage unit blocks in the co-located block thatcorresponds to the current block as the temporal reference blockcandidates. Here, 4 blocks may be the top left center block (block No.0), the top right center block (block No. 1), the bottom right centerblock (block No. 2), and the bottom left center block (block No. 3).

As an example, the encoder and the decoder may perform scanning in theorder of block No. 0→block No. 1→block No. 2→block No. 3. The order ofscanning the temporal reference block candidates may be determineddifferently from the order of the numbers illustrated on 2110 of FIG.21. For example, the encoder and the decoder may perform the scanning inthe order of No. 2→block No. 3→block No. 0→block No. 1.

Referring to 2120 of FIG. 21, the encoder and the decoder may use 16blocks among the storage unit blocks in the co-located block thatcorresponds to the current block as the temporal reference blockcandidates.

As an example, the encoder and the decoder may perform scanning in theorder of block No. 0→block No. 1→block No. 2→block No. 3→block No.4→block No. 5→block No. 6→block No. 7→block No. 8→block No. 9→block No.10→block No. 11→block No. 12→block No. 13→block No. 14→block No. 15. Theorder of scanning the temporal reference block candidates may bedetermined differently from the order of the numbers illustrated on 2120of FIG. 21. For example, the encoder and the decoder may perform thescanning in the order of block No. 2→block No. 3→block No. 0→block No.1→block No. 10→block No. 11→block No. 12→block No. 13→block No. 14→blockNo. 15→block No. 4→block No. 5→block No. 6→block No. 7→block No. 8→blockNo. 9.

The positions of the temporal reference block candidates and/or temporalmotion vector predictor candidates are not limited to the inside of thecurrent block and the co-located block, but may be outside of a boundaryof the current block and/or the co-located block. Further, the scanningorder (priority) of the temporal reference block candidates existingoutside the current block and/or the co-located block may be faster(higher) than the scanning order (priority) of the temporal referenceblock candidates existing inside the current block and/or the co-locatedblock. An embodiment thereof will be described later with reference toFIG. 22.

The number, the position, and the scanning order of the temporalreference block candidates (or temporal motion vector predictorcandidates) are not limited to the above-described embodiments, but maybe differently determined depending on the implementation and/or need.For example, if the size of the current block and the co-located blockis 32×32 and the size of the storage unit block is 16×16, the maximumnumber of temporal reference block candidates and/or temporal motionvector predictor candidates may be 4. Further, in the case where thesize of the current block and the co-located block is smaller than thesize of the storage unit block, the above-described scanning method maynot be used.

FIG. 22 is a conceptual diagram schematically illustrating still anotherembodiment of a method for deriving a temporal motion vector predictor.2210 and 2220 of FIG. 22 illustrate blocks which appear when the currentblock and the co-located block overlap each other.

In FIG. 22, the respective blocks constituting the co-located block mayrepresent the storage unit blocks. That is, the respective blocks in theco-located block may represent a unit in which the motion information iscompressed and stored, and one piece of motion information may be storedin each block in the co-located block. In an embodiment of FIG. 22, forconvenience of explanation, it is assumed that the size of the storageunit of the motion information, that is, the size of the storage unitblock, is 16×16, and the size of the current block and the co-locatedblock is 64×64.

As described above, the encoder and the decoder may select the storageunit block located inside and/or outside of the co-located block as thetemporal reference block for the current block. The encoder and thedecoder may derive the motion vector of the selected temporal referenceblock, and determine the derived motion vector as the temporal motionvector predictor. At this time, the encoder and the decoder may derivethe temporal motion information predictor from the prediction unit colPuin the reference picture, which has the same motion information as thetemporal reference block.

As an embodiment, referring to 2210 of FIG. 22, the encoder and thedecoder may use the bottom right corner block (block No. 0) 2214 and thetop left center block (block No. 1) 2212 as the temporal reference blockcandidate and/or temporal motion vector predictor candidate for thecurrent block. At this time, the encoder and the decoder may scan thetemporal reference block candidate in the order of the bottom rightcorner block 2214→top left center block 2212 and use the motion vectorof the available first block (block having high scanning priority) asthe temporal motion vector predictor for the current block.

First, the encoder and the decoder may check whether the bottom rightcorner block 2214 is available. An example of the case where the bottomright corner block 2214 is unavailable may be the case where the bottomright corner block 2214 does not include available motion information,the case where the bottom right corner block 2214 and/or thecorresponding colPu is coded in the intra mode, or the case where colPuis unavailable.

If the bottom right corner block 2214 is available, the encoder and thedecoder may select the bottom right corner block 2214 as the temporalreference block. At this time, the motion vector of the bottom rightcorner block 2214 may be determined as the temporal motion vectorpredictor. If the bottom right corner block 2214 is unavailable, theencoder and the decoder may select the top left center block (block No.1) 2212 as the temporal reference block. At this time, the motion vectorof the top left center block 2212 may be determined as the temporalmotion vector predictor.

As described above, in the case where the bottom right corner block 2214and the top left center block 2212 are used as the temporal referenceblock candidate and/or temporal motion vector predictor candidate, adetailed embodiment of a method for guiding colPu is as follows. In theembodiment to be described later, it is assumed that the motioninformation of the minimum unit block that is located on the topleftmost side in the storage unit block is used as the representativemotion information.

First, the encoder and the decoder may derive colPu corresponding to thebottom right corner block 2214. For this, the encoder and the decodermay specify the bottom right corner block 2214 by the coordinates of thepixels included in the current block and/or co-located block. At thistime, the bottom right corner block 2214 may be specified by thecoordinates of (xP+nPSW, yP+nPSW). This may be represented as follows.

-   -   Variable colPu and its position (xPCol, yPCol) are derived in        the following ordered steps:        -   Right-bottom luma position of the current prediction unit is            defined by            xPRb=xP+nPSW            yPRb=yP+nPSH

Here, xPRb and yPRb may represent the coordinates specified by thetemporal reference block. xP and yP may represent the coordinates of thetop leftmost pixel in the current block, mPSW may represent the width ofthe current block, and nPSH may represent the height of the currentblock.

If the bottom right corner block 2214 is specified, the encoder and thedecoder may specify the position of the minimum unit block in the bottomright corner block 2214, in which the representative motion vector isstored. Here, the position of the minimum unit block may be specified bythe coordinates of ((xPRb>>4)<<4, (yPRb>>4)<<4). At this time, colPu maybe specified by the prediction unit in the reference picture, whichincludes the coordinates of ((xPRb>>4)<<4, (yPBr>>4)<<4). This may berepresented as follows.

-   -   the variable colPu is set as the prediction unit covering the        modified position given by ((xPRb>>4)<<4, (yPRb>>4)<<4) inside        the colPic

Here, if colPu is coded in the inter mode and is available, the motionvector of colPu may be used as the temporal motion vector predictor forthe current block. This may correspond to the case where the bottomright corner block 2214 is selected as the temporal reference block.However, if the colPu is coded in the intra mode or is unavailable, theencoder and the decoder may specify the top left center block 2212 bythe coordinates of the pixels included in the current block and theco-located block. At this time, the top left center block 2212 may bespecified by the coordinates of (xP+(nPSW>>1)−1, yP+(nPSW>>1)−1). Thismay be represented as follows.

-   -   If colPu is coded in an intra prediction mode or colPu is        unavailable, the following applies.        -   Center luma position of the current prediction unit is            defined by            xPCtr=xP+(nPSW>>1)−1            yPCtr=yP+(nPSH>>1)−1

Here, xPCtr and yPCtr may represent the coordinates specified by thetemporal reference block.

If the top left center block 2212 is specified, the encoder and thedecoder may specify the position of the minimum unit block in the topleft center block 2212, in which the representative motion vector isstored. Here, the position of the minimum unit block may be specified bythe coordinates of ((xPCtr>>4)<<4, (yPCtr>>4)<<4). At this time, thecolPu may be specified by the prediction unit in the reference picture,which includes the coordinates of ((xPCtr>>4)<<4, (yPCtr>>4)<<4). Thismay correspond to the case where the top left center block 2212 isselected as the temporal reference block, and may be represented asfollows.

-   -   The variable colPu is set as the prediction unit covering the        modified position given by ((xPCtr>>4)<<4, (yPCtr>>4)<<4) inside        the colPic.

At this time, the top leftmost coordinates in colPu may be representedby (xPCol, xPCol) as follows.

-   -   (xPCol, yPCol) is set equal to the top-left luma sample of the        colPu relative to the top-left luma sample of the colPic.

As another embodiment, referring to 2220 of FIG. 22, the encoder and thedecoder may use the bottom right corner block (block No. 0) 2224 and thebottom right center block (block No. 1) 2222 as the temporal referenceblock candidate and/or temporal motion vector predictor candidate forthe current block. At this time, the encoder and the decoder may scanthe temporal reference block candidate in the order of the bottom rightcorner block 2224→bottom right center block 2222 and use the motionvector of the available first block (block having high scanningpriority) as the temporal motion vector predictor for the current block.

First, the encoder and the decoder may check whether the bottom rightcorner block 2224 is available. An example of the case where the bottomright corner block 2224 is unavailable may be the case where the bottomright corner block 2224 does not include available motion information,the case where the bottom right corner block 2224 and/or thecorresponding colPu is coded in the intra mode, or the case where colPuis unavailable.

If the bottom right corner block 2224 is available, the encoder and thedecoder may select the bottom right corner block 2224 as the temporalreference block. At this time, the motion vector of the bottom rightcorner block 2224 may be determined as the temporal motion vectorpredictor. If the bottom right corner block 2224 is unavailable, theencoder and the decoder may select the bottom right center block (blockNo. 1) 2222 as the temporal reference block. At this time, the motionvector of the bottom right center block 2222 may be determined as thetemporal motion vector predictor.

As described above, in the case where the bottom right corner block 2224and the bottom right center block 2222 are used as the temporalreference block candidate and/or temporal motion vector predictorcandidate, a detailed embodiment of a method for guiding colPu is asfollows. In the embodiment to be described later, it is assumed that themotion information of the minimum unit block that is located on the topleftmost side in the storage unit block is used as the representativemotion information.

First, the encoder and the decoder may derive colPu corresponding to thebottom right corner block 2224. For this, the encoder and the decodermay specify the bottom 2 b right corner block 2214 by the coordinates ofthe pixels included in the current block and the co-located block. Atthis time, the bottom right corner block 2224 may be specified by thecoordinates of (xP+nPSW, yP+nPSW). This may be represented as follows.

-   -   Variable colPu and its position (xPCol, yPCol) are derived in        the following ordered steps:        -   Right-bottom luma position of the current prediction unit is            defined by            xPRb=xP+nPSW            yPRb=yP+nPSH

If the bottom right corner block 2224 is specified, the encoder and thedecoder may specify the position of the minimum unit block in the bottomright corner block 2224, in which the representative motion vector isstored. Here, the position of the minimum unit block may be specified bythe coordinates of ((xPRb>>4)<<4, (yPRb>>4)<<4). At this time, colPu maybe specified by the prediction unit in the reference picture, whichincludes the coordinates of ((xPRb>>4)<<4, (yPBr>>4)<<4). This may berepresented as follows.

-   -   the variable colPu is set as the prediction unit covering the        modified position given by ((xPRb>>4)<<4, (yPRb>>4)<<4) inside        the colPic.

Here, if colPu is coded in the inter mode and is available, the motionvector of colPu may be used as the temporal motion vector predictor forthe current block. This may correspond to the case where the bottomright corner block 2224 is selected as the temporal reference block.However, if the colPu is coded in the intra mode or is unavailable, theencoder and the decoder may specify the bottom right center block 2222by the coordinates of the pixels included in the current block and theco-located block. At this time, the bottom right center block 2222 maybe specified by the coordinates of (xP+(nPSW>>1), yP+(nPSW>>1)). Thismay be represented as follows.

-   -   If colPu is coded in an intra prediction mode or colPu is        unavailable, the following applies.        -   Center luma position of the current prediction unit is            defined by            xPCtr=xP+(nPSW>>1)            yPCtr=yP+(nPSH>>1)

If the bottom right center block 2222 is specified, the encoder and thedecoder may specify the position of the minimum unit block in the bottomright center block 2222, in which the representative motion vector isstored. Here, the position of the minimum unit block may be specified bythe coordinates of ((xPCtr>>4)<<4, (yPCtr>>4)<<4). At this time, thecolPu may be specified by the prediction unit in the reference picture,which includes the coordinates of ((xPCtr>>4)<<4, (yPCtr>>4)<<4). Thismay correspond to the case where the bottom right center block 2222 isselected as the temporal reference block, and may be represented asfollows.

-   -   The variable colPu is set as the prediction unit covering the        modified position given by ((xPCtr>>4)<<4, (yPCtr>>4)<<4) inside        the colPic.

At this time, the top leftmost coordinates in colPu may be representedby (xPCol, xPCol) as follows.

-   -   (xPCol, yPCol) is set equal to the top-left luma sample of the        colPu relative to the top-left luma sample of the colPic.

As still another embodiment, the encoder and the decoder may checkwhether the positions (or coordinates) of the temporal reference blockcandidate and/or colPu correspond to the coordinates in the LCU to whichthe current block belongs when checking the availability of the temporalreference block candidate. If the positions (or coordinates) of thetemporal reference block candidate and/or colPu are not included in theLCU to which the current block belongs, the encoder and the decoder mayconsider that the temporal reference block candidate and/or colPu areunavailable.

In the embodiments of the co-located block of 2210 and 2220 as describedabove, the encoder and the decoder may check whether the bottom rightcorner block is available. If the bottom right corner block isavailable, the motion vector of the bottom right corner block may beused as the temporal motion vector predictor, and if the bottom rightcorner block is unavailable, the motion vector of the top left centerblock or the bottom right center block may be used as the temporalmotion vector predictor. At this time, if the positions (or coordinates)of the bottom right corner block and/or the corresponding colPu areoutside the boundary of the ICU to which the current block belongs, theencoder and the decoder may consider that the bottom right corner blockand/or the corresponding colPu are unavailable. That is, if thepositions (or coordinates) of the bottom right corner block and/or thecorresponding colPu are outside the boundary of the LCU to which thecurrent block belongs, the encoder and the decoder may determine themotion vector of the top left center block or the bottom right centerblock as the temporal motion vector predictor.

As described above, in the case of checking the availability of thetemporal reference block candidate and/or colPu based on the LCU, adetailed embodiment of a method for guiding colPu is as follows. In theembodiment to be described later, it is assumed that the motioninformation of the minimum unit block located on the top leftmost sidein the storage unit block is used as the representative motioninformation.

First, the encoder and the decoder may derive colPu corresponding tobottom right corner block. This may be represented as follows.

-   -   Variable colPu and its position (xPCol, yPCol) are derived in        the following ordered steps:        -   Right-bottom luma position of the current prediction unit is            defined by            xPRb=xP+nPSW            yPRb=yP+nPSH    -   the variable colPu is set as the prediction unit covering the        modified position given by ((xPRb>>4)<<4. (yPRb>>4)<<4) inside        the colPic.

Here, if colPu is coded in the inter mode, is available, and is locatedon the coordinates in the LCU to which the current block belongs, themotion vector of colPu may be used as the temporal motion vectorpredictor for the current block. This may correspond to the case wherethe bottom right corner block is selected as the temporal referenceblock.

However, if the colPu is coded in the intra mode or is unavailable, orthe position (or coordinates) of the colPu is outside the boundary ofthe LCU to which the current block belongs, the encoder and the decodermay derive the colPu that corresponds to the top left center block (orbottom right center block). This may correspond to the case where thetop left center block (or bottom right center block) is selected as thetemporal reference block, and may be represented as follows.

-   -   If colPu is coded in an intra prediction mode or colPu is        unavailable or not in the current LCU, the following applies.        -   Center luma position of the current prediction unit is            defined by            xPCtr=xP+(nPSW>>1)−1 or xPCtr=xP+(nPSW>>1)            yPCtr=yP+(nPSH>>1)−1 or yPCtr=yP+(nPSH>>1)        -   The variable colPu is set as the prediction unit covering            the modified position given by ((xPCtr>>4)<<4,            (yPCtr>>4)<<4) inside the colPic.

At this time, the top leftmost coordinates in the colPu may berepresented by (xPCol, xPCol) as follows.

-   -   (xPCol, yPCol) is set equal to the top-left luma sample of the        colPu relative to the top-left luma sample of the colPic.

In the case of checking the availability of the temporal reference blockcandidate and/or colPu based on the LCU, still another embodiment of themethod for deriving the colPu is as follows.

First, if the position (or coordinates) of the bottom right corner blockis inside the LCU to which the current block belongs, the encoder andthe decoder may derive the colPu corresponding to the bottom rightcorner block. If the position (or coordinates) of the bottom rightcorner block is outside the boundary of the LCU to which the currentblock belongs, the colPu may be considered to be unavailable. This maybe represented as follows.

-   -   Variable colPu and its position (xPCol, yPCol) are derived in        the following ordered steps:        -   1. The variable colPu is derived as follows            yPRb=yP+nPSH        -   If (yP>>Log 2MaxCuSize) is equal to (yPRb>>Log 2MaxCuSize),            the horizontal component of the right-bottom luma position            of the current prediction unit is defined by            xPRb=xP+nPSW        -   and the variable colPu is set as the prediction unit            covering the modified position given by ((xPRb>>4)<<4,            (yPRb>>4)<<4) inside the colPic.        -   Otherwise ((yP>>Log 2MaxCuSize) is not equal to (yPRb>>Log            2MaxCuSize)), colPu is marked as unavailable.

Here, if the colPu is coded in the inter mode and is available, themotion vector of the colPu may be used as the temporal motion vectorpredictor for the current block. This may correspond to the case wherethe bottom right corner block is selected as the temporal referenceblock. However, if the colPu is coded in the intra mode or isunavailable, the encoder and the decoder may derive the colPu thatcorresponds to the bottom right center block. This may correspond to thecase where the bottom right center block is selected as the temporalreference block, and may be represented as follows.

-   -   2. When colPu is coded in an intra prediction mode or colPu is        unavailable, the following applies.        -   Central luma position of the current prediction unit is            defined by            xPCtr=(xP+(nPSW>>1)            yPCtr=(yP+(nPSH>>1)        -   The variable colPu is set as the prediction unit covering            the modified position given by ((xPCtr>>4)<<4,            (yPCtr>>4)<<4) inside the colPic.

At this time, the top leftmost coordinates in the colPu may berepresented by (xPCol, xPCol) as follows.

-   -   3. (xPCol, yPCol) is set equal to the top-left luma sample of        the colPu relative to the top-left luma sample of the colPac.

FIG. 23 is a flowchart schematically illustrating a method for interprediction according to an embodiment of the present invention.

Referring to FIG. 23, the encoder and the decoder may store the temporalmotion information of the reference picture (S2310). At this time, inorder to reduce the size of the required memory, the encoder and thedecoder may compress and store the temporal motion information. Sincethe embodiments of the method for compressing the temporal motioninformation have been described with reference to FIGS. 7 to 15,explanation thereof will be omitted.

Further, the encoder and the decoder may select the temporal referenceblock for the current block from the reference picture (S2320). Here,the temporal reference block may mean the storage unit block in thereference picture, which includes the motion vector that is used as thetemporal motion vector predictor.

The position of the temporal reference block may be determined based onthe current block and/or the co-located block for the current block. Theencoder and the decoder may select the block in the predeterminedposition in the reference picture as the temporal reference block forthe current block and select the temporal reference block among apredetermined number of temporal reference block candidates. Theselected temporal reference block may be specified as the coordinates ofthe pixel included in the temporal reference block rather than the blockitself.

Since the embodiments of the method for deriving the temporal referenceblock have been described with reference to FIGS. 16 to 22, explanationthereof will be omitted.

If the temporal reference block is selected and/or specified, theencoder and the decoder may derive the temporal motion vector predictorfor the current block using the temporal reference block (S2330).

The encoder and the decoder may derive the motion vector of the temporalreference block. At this time, the derived motion vector may bedetermined as the temporal motion vector predictor. Since the temporalreference block may correspond to the storage unit, the encoder and thedecoder may derive the temporal motion information predictor from theprediction unit (for example, colPu) having the same motion informationas the temporal reference block.

If the temporal motion vector predictor for the current block isderived, the encoder and the decoder may perform the inter prediction onthe current block using the derived temporal motion vector predictor(S2340).

In the above-described embodiments, the methods are described based onthe flowcharts as a series of steps or blocks. However, the presentinvention is not limited to the disclosed order of steps, and a certainstep may occur simultaneously with or in an order different from that ofother steps. Further, those of skilled in the art will be able tounderstand that steps shown in the flowchart are not exclusive, othersteps can be included, or that one or more steps in the flowchart can bedeleted without exerting an influence on the scope of the presentinvention.

The above-described embodiments include various types of examples.Although all possible combinations for presenting various types ofexamples are unable to be described, those of ordinary skill in the artwill be able to recognize that other combinations are possible.Accordingly, the present invention can include all other substitutions,corrections, and modifications that belong to the following claims.

While the invention has been shown and described with reference tocertain embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail may be made thereinwithout departing from the spirit and scope of the present invention, asdefined by the appended claims.

The invention claimed is:
 1. A method of video decoding by a decoding apparatus, the method comprising: deriving a spatial motion vector predictor candidate for the current block based on a spatial neighboring block of a current block in a current picture; deriving a temporal motion vector predictor candidate for the current block; deriving a motion vector of the current block based on the spatial motion vector predictor candidate and the temporal motion vector predictor candidate; deriving a predicted pixel of the current block based on the motion vector of the current block; and generating a reconstructed picture based on the predicted pixel, wherein deriving the temporal motion vector predictor candidate comprises: determining a reference prediction unit (colPu) which is a prediction block encompassing a modified location (x, y); and deriving the temporal motion vector predictor candidate based on motion information of the colPu in a reference picture, wherein the modified location is specified by a position ((xPCtr>>4)<<4, (yPCtr>>4)<<4), wherein a position (xPCtr, yPCtr) is a position of a pixel located at the bottom right side among four central pixels of a co-located block, and wherein the co-located block is a block with a same position and a same size as the current block and is located in the reference picture.
 2. The method of claim 1, wherein the position (xPCtr, yPCtr) is specified by xPCtr=xP+(nPSW>>1), yPCtr=yP+(nPSH>>1), a position (xP, yP) is a position of top left sample of the current block, nPSW and nPSH are width and height of the current block respectively.
 3. The method claim 1, wherein based on a bottom right pixel not belonging to a largest coding unit (LCU) to which the co-located block belongs, the modified location is specified by the position ((xPCtr>>4)<<4, (yPCtr>>4)<<4), and wherein the bottom right pixel neighbors the co-located block and is located at a lower right side of the co-located block.
 4. The method of claim 3, wherein a position of the bottom right pixel is (xPRB, yPRB), wherein xPRB=xP+nPSW and yPRB=yP+nPSH, wherein (xP, yP) is a position of a top left sample of the current block, nPSW and nPSH are width and height of the current block, respectively.
 5. The method of claim 4, wherein when the yP and the yPRB are not in the same LCU, the bottom right pixel is determined as not belonging to the LCU to which the co-located block belongs.
 6. The method of claim 1, wherein based on a bottom right pixel which is not available, the modified location is specified by the position ((xPCtr>>4)<<4, (yPCtr>>4)<<4), and wherein the bottom right pixel neighbors the co-located block and is located at a lower right side of the co-located block.
 7. The method of claim 1, wherein based on an intra colPu which is derived based on a bottom right pixel and is an intra coded prediction block, the modified location is specified by the position ((xPCtr>>4)<<4, (yPCtr>>4)<<4), and wherein the bottom right pixel neighbors the co-located block and is located at a lower right side of the co-located block.
 8. The method of claim 7, wherein the intra colPu encompasses a position ((xPRB>>4)<<4, (yPRB>>4)<<4), wherein a position (xPRB, yPRB) is a position of the bottom right pixel.
 9. A method of video encoding by a encoding apparatus, the method comprising: deriving a spatial motion vector predictor candidate for the current block based on a spatial neighboring block of a current block in a current picture; deriving a temporal motion vector predictor candidate for the current block; deriving a motion vector of the current block based on the spatial motion vector predictor candidate and the temporal motion vector predictor candidate; deriving a predicted pixel of the current block based on the motion vector of the current block; generating a residual pixel based on the predicted pixel of the current block; and generating a bitstream including information on the residual pixel, wherein deriving the temporal motion vector predictor candidate comprises: determining a reference prediction unit (colPu) which is a prediction block encompassing a modified location (x, y); and deriving the temporal motion vector predictor candidate based on motion information of the colPu in a reference picture, wherein the modified location is specified by a position ((xPCtr>>4)<<4, (yPCtr>>4)<<4), wherein a position (xPCtr, yPCtr) is a position of a pixel located at the bottom right side among four central pixels of a co-located block, and wherein the co-located block is a block with a same position and a same size as the current block and is located in the reference picture.
 10. A non-transitory computer readable storage medium storing information on instructions, when executed, causing a video decoding apparatus to perform operations comprising: deriving a spatial motion vector predictor candidate for the current block based on a spatial neighboring block of a current block in a current picture; deriving a temporal motion vector predictor candidate for the current block; deriving a motion vector of the current block based on the spatial motion vector predictor candidate and the temporal motion vector predictor candidate; deriving a predicted pixel of the current block based on the motion vector of the current block; and generating a reconstructed picture based on the predicted pixel, wherein deriving the temporal motion vector predictor candidate comprises: determining a reference prediction unit (colPu) which is a prediction block encompassing a modified location (x, y); and deriving the temporal motion vector predictor candidate based on motion information of the colPu in a reference picture, wherein the modified location is specified by a position ((xPCtr>>4)<<4, (yPCtr>>4)<<4), wherein a position (xPCtr, yPCtr) is a position of a pixel located at the bottom right side among four central pixels of a co-located block, and wherein the co-located block is a block with a same position and a same size as the current block and is located in the reference picture. 